The SurirelloideÆ are usually understood to include the genera Surirella, Podocystis, Cymatopleura and Campylodiscus, all of which resemble each other more or less, either in having a keel or markings like the divisions of the keel in Surirella and a median line, or pseudoraphe. The genus Nitzschia also has a keel, but it does not border each side of the valve as in Surirella, being found either near one margin or between it and the centre. Certain of the SurirellÆ are allied to the group Tryblionella of the NitzschiÆ, while forms of Stenopterobia are distinguished with difficulty from the group Sigmata.

The following arrangement, therefore, is intended to include all genera having a keel or something which resembles it.

Hantzschia.—Valve asymmetrical; keels of the two valves opposite each other.

Nitzschia.—Valve asymmetrical; keels not (usually) opposite each other.

Surirella.—Valve usually symmetrical; a keel on each border.

Cymatopleura.—Valve without an elevated keel, but with markings like those of Surirella; undulated in zone view.

Campylodiscus.—Valves saddle-shaped.

Hantzschia GRUN. (1877)

(named after C. A. Hantzsch)

Valve arcuate, with rostrate ends; keel puncta short, prolonged into costÆ or extending across the valve; median nodule rudimentary; the keels of the two valves opposite each other.

Distinguished from Nitzschia chiefly by the position of the keels. According to Mereschkowsky, however, two species of Nitzschia, N. lanceolata and N. spectabilis, show the same peculiarity.

Chromatophores four, two on each of the zones (Mereschkowsky).

HANTZSCHIA AMPHIOXYS (EHR.) GRUN.

Valve slightly arcuate, with rostrate apices; keel puncta, 8 in 10 µ; striÆ transverse, 16-18 in 10 µ, punctate. L. 60 µ.

Quite variable.

Fresh water.

Pl. 32, Fig. 9.

HANTZSCHIA AMPHIOXYS VAR. MAJOR GRUN.

Valve as in type, but the keel puncta are 5 in 10 µ and the striÆ are 11-12 in 10 µ. L. 71 µ.

H. amphioxys var. major Grun. is stated to be 120 µ in length. The present form is smaller but corresponds in puncta and striation. Van Heurck remarks that it approaches H. virgata.

Abundant in sand ripples on the beach at Cape May, N. J.

Pl. 39, Fig. 4.

Fig. 6, Pl. 39, is drawn from an authentic specimen of Wm. Smith's Nitzschia amphioxys, from England, and is introduced for comparison. The central nodule is not evident.

Fig. 3, Pl. 39, is from a specimen from an unknown locality. The keel puncta are 6 and the striÆ 16 in 10 µ.

HANTZSCHIA VIRGATA (ROPER) GRUN.

Valve arcuate on the dorsal side, nearly straight on the ventral side, with rostrate, recurved apices; keel puncta prolonged to one-third the width of the valve, 4 in 10 µ; transverse striÆ, 9-10 in 10 µ. L. 115 µ.

Shark River, N. J. (Kain).

I have not been able to find this form on our coast. The figure is drawn from a specimen from another locality.

Pl. 32, Fig. 23.

HANTZSCHIA MARINA (DONK.) GRUN.

Valve with dorsal margin slightly arcuate, ventral margin straight; apices rostrate and recurved; keel puncta, 6 in 10 µ, prolonged into costÆ across the entire valve; transverse striÆ, 12 in 10 µ, in double rows of alternating puncta between the costÆ. L. 106 µ.

Epithemia marina Donkin.

Along the coast.

Pl. 32, Fig. 22.

Nitzschia HASSALL (1845), em. GRUN. (1880)

(named after Christian L. Nitzsch, of Halle)

Frustules usually free, sometimes enclosed in tubes or united into a filament. Valves keeled, the keels of the two valves usually diagonally opposite (see Hantzschia); keel puncta short or prolonged.

According to Mereschkowsky, there are at least two endochrome plates placed transversely on the zones; sometimes there are from four to six plates, in one species twenty granules and in another no trace of any endochrome whatever.

The following analysis is that of Grunow as given in Cleve and Grunow's "Arctic Diatoms," and adopted and illustrated by Van Heurck in his "Synopsis."

GROUPS

1. Tryblionella.—Keel very excentric, valve often folded; keel puncta indistinct, usually the same in number as the striÆ.

2. Panduriformes.—Valve broad, constricted in the middle, with more or less evident fold; keel very near the edge; keel puncta quite evident or apparently wanting.

3. ApiculatÆ.—Keel very near the edge; valve linear or somewhat narrower in the middle; striÆ on the longitudinal fold fainter than on the remaining surface, or wanting; puncta not in quincunx.

4. Pseudo-Tryblionella.—Keel more or less close to the edge; valve with a more or less deep longitudinal fold over which the striÆ are spread in the same way as over the remaining surface; keel puncta always distinct.

5. CircumsutÆ.—Valve with more or less wide longitudinal fold; keel very excentric; keel puncta quite evident; surface of valve irregularly punctate and also traversed by rows of delicate puncta which belong to a different layer of the valve.

6. DubiÆ.—Like the group Pseudo-Tryblionella, but the valves are not so much folded; frustules sometimes narrowed in the middle. The separation of species is difficult and, in part, doubtful. Keel excentric.

7. BilobatÆ.—Like the group DubiÆ, but with more central keel and so forming a transition to the group Pseudo-Amphiprora; valves without longitudinal folds.

8. Pseudo-Amphiprora.—Valve with quite central, sharp keel, arcuate, without longitudinal fold; keel puncta always evident; frustule narrowed in the middle with more or less marked central nodule.

Includes two species not found in this locality.

9. Perrya.—Valve arched with very sharp central keel; not narrowed in the middle; keel puncta mostly on short or long lines which are sometimes interrupted.

Includes six species not found in this locality.

10. EpithemioideÆ.—Keel excentric; keel puncta extended into costÆ across the entire valve.

11. Grunowia.—As in the group EpithemioideÆ, except that the costÆ are shorter, not extending across the valve; keel very excentric.

12. Scalares.—Like Grunowia, but with sharper, somewhat excentric keel; transverse section of frustule quadrangular.

13. Insignes.—Like Scalares, but with more central keel so that many of the forms are near the group Perrya; frustule somewhat sigmoid.

14. Bacillaria.—Keel central or nearly so; valve somewhat arched; keel sharp, as in the group Insignes.

15. Vivaces.—Keel moderately excentric; valve, according to position, semi-lanceolate, with keel puncta in short rows, or lanceolate with quite central keel. The valves have in many positions a resemblance to Hantzschia, so that N. vivax frequently becomes confounded with a form of H. amphioxys. The median keel puncta are not distant and a central nodule is not evident as is the case in all species of Hantzschia.

16. SpathulatÆ.—Like the group Bacillaria, but usually with very delicate striated valves; keel in valve view usually bordered with two parallel lines.

17. DissipatÆ.—Like Vivaces and SpathulatÆ, but with smaller central keel and without parallel lines. Valves usually small, very delicately striated; no central nodule.

18. SigmoideÆ.—Keel quite central; no parallel lines; frustule sigmoid; valve without longitudinal furrow; keel puncta not extended; no central nodule evident.

19. Sigmata.—Like SigmoideÆ, but with a more excentric keel.

20. ObtusÆ.—Like Sigmata, with a more or less excentric keel which has in the middle a small bending to the inside; middle keel puncta somewhat more distant than the others, and between them a central nodule evident.

21. Spectabiles.—Valve large, slightly arcuate, with excentric keel; no longitudinal folds; keel puncta somewhat extended over the valve but much less than in the group Insignes, and often scarcely perceptible.

22. Lineares.—Keel somewhat excentric, but less than in Spectabiles; frustule straight, sometimes a little constricted in the middle, so that a transition is shown to the groups DubiÆ and BilobatÆ. Valve without longitudinal fold; keel puncta round or somewhat angular, scarcely extended.

23. LanceolatÆ.—Valve lanceolate, linear-lanceolate or rarely elliptical, with very excentric keel; not folded; keel puncta not extended.

24. Nitzschiella.—Valve with excentric keel and long, produced apices.

Tryblionella

NITZSCHIA TRYBLIONELLA HANTZSCH

Valve elliptical-lanceolate, with subacute apices; longitudinal fold well marked; striÆ coarse, transverse, 5 in 10 µ; indistinct puncta intermediate between the striÆ. L. 45 µ. Quite variable.

Blue clay.

Pl. 32, Fig. 8.

NITZSCHIA GRANULATA GRUN.

Valve elliptical or elliptical-lanceolate; striÆ in double rows, each row of three or four small puncta along the margin and rows of large puncta about 6 in 10 µ across the valve. L. 28-44 µ.

Blue clay. Along the coast.

Pl. 32, Fig. 3.

NITZSCHIA NAVICULARIS (BRÉB.) GRUN.

Valve elliptical-lanceolate, with acute apices; striÆ on one side a double row of large and small puncta, and on the other side radiate short rows of large puncta, 7 in 10 µ; middle of valve hyaline. L. 35-60 µ.

Blue clay. Not common.

Pl. 32, Fig. 4.

NITZSCHIA COMPRESSA (BAIL.)

Valve elliptical-lanceolate, sometimes acuminate; striÆ, 6 or 7 in 10 µ, coarsely punctate. L. 56 µ.

Pyxidicula compressa Bailey.

Nitzschia punctata (Wm. Sm.) Grun.

Tryblionella punctata Wm. Sm.

Common along the coast.

Pl. 39, Fig. 7.

Var. minor (H. L. Smith).—Valve acuminate; striÆ, 8 in 10 µ. L. 22 µ.

Pyxidicula compressa var. minor H. L. Smith, Type Slide No. 431.

Pl. 39, Fig. 8.

The smaller forms occur northward, while the larger are found southward. This is unquestionably Bailey's form, as indicated by his figure and by the fact that it is found everywhere along the coast. Wm. Smith's T. punctata is the same species, although the puncta are smaller.

Panduriformes

NITZSCHIA PANDURIFORMIS GREG.

Valve elliptical, constricted in the middle, with sub-cuneate apices; longitudinal fold, with a punctate longitudinal line; striÆ transverse and oblique, 15 in 10 µ; keel puncta, 6 in 10 µ. L. 108 µ.

Along the coast. More often found southward.

Pl. 39, Fig. 2.

NITZSCHIA PANDURIFORMIS VAR. MINOR GRUN.

Valve elliptical, constricted in the middle, with cuneate apices; keel puncta, 9 in 10 µ; striÆ in transverse and oblique lines about 20 in 10 µ; longitudinal fold bordered by a punctate line. L. 34 µ.

Pavonia, N. J., artesian well.

Pl. 32, Fig. 5.

The var. continua Grun. is reported as occurring in Shark River. It varies in having the longitudinal fold punctate. It is also usually smaller than var. minor.

ApiculatÆ

NITZSCHIA APICULATA (GREG.) GRUN.

Valve oblong-linear, with cuneate-apiculate apices; striÆ punctate, apparently interrupted or pervious, about 18 in 10 µ. L. 26 µ.

Chester River, Md.

Pl. 32, Fig. 6.

The puncta are continued across the valve, but are less distinct on the fold. The figure shows the entire frustule with the fold on each valve. The valves are sometimes slightly constricted.

NITZSCHIA ACUMINATA (WM. SM.) GRUN.

Valve linear, sometimes slightly constricted in the middle, with acuminate apices; longitudinal fold entirely without or with indistinct striÆ; keel puncta not evident; striÆ, 14-15 in 10 µ. L. 82 µ.

Port Penn, Delaware River.

Pl. 32, Fig. 13.

NITZSCHIA PLANA WM. SM.

Valve linear; apices acute, slightly constricted in the middle; longitudinal fold further from the keel than the margin, broad, with scattered puncta; striÆ subtle, irregular, interrupted, about 18 in 10 µ; keel puncta oblong, 3-6 in 10 µ. L. 100-170 µ.

Blue clay. Along the coast.

Pl. 32, Fig. 2.

Pseudo-Tryblionella

NITZSCHIA LITORALIS VAR. DELAWARENSIS GRUN.

Valve linear, with obtusely rounded cuneate ends, scarcely, if at all, constricted in the middle; longitudinal fold wide; keel puncta, 5 or 6 in 10 µ, sometimes confluent; striÆ obscure, about 21 in 10 µ. L. 75 µ.

Delaware River.

Pl. 32, Fig. 12.

This form is drawn from a slide of Christian Febiger containing an abundance of specimens from Delaware City, and marked "Nitzschia dubia."

CircumsutÆ

NITZSCHIA CIRCUMSUTA (BAIL.) GRUN.

Valve elliptical, sometimes more than 200 µ in length; longitudinal fold more or less conspicuous; keel puncta about 4 in 10 µ, the middle distant with the appearance of a nodule; striÆ irregular, subtle, finely punctate, frequently interrupted.

Surirella circumsuta Bail.

Tryblionella scutellum Wm. Sm.

Common in brackish water.

Pl. 32, Fig. 1.

DubiÆ

NITZSCHIA DUBIA WM. SM.

Valve linear, scarcely, if at all, constricted in the middle, with cuneate, produced, apiculate apices, somewhat recurved; keel very excentric; puncta sometimes partly prolonged, about 9 in 10 µ; striÆ, 20-24 in 10 µ. L. 93 µ.

Reported from along the New Jersey coast. I have not seen it. It is generally regarded as fresh-water. Slides sometimes labelled N. dubia are in reality N. litoralis var. delawarensis.

Pl. 39, Fig. 5.

The figure is drawn from a specimen from another locality.

BilobatÆ

NITZSCHIA BILOBATA WM. SM.

Valve linear-lanceolate, constricted in the middle, apiculate at the ends; keel puncta 6 in 10 µ, prolonged unequally across part of the valve, the two median sub-remote; striÆ, 16 in 10 µ. Frustule oblong, truncate, constricted in the middle. L. 120 µ.

Shark River, N. J., Chester River, Md.

Pl. 32, Figs. 10 and 11.

EpithemioideÆ

NITZSCHIA EPITHEMIOIDES GRUN.

Valve linear, with cuneate, rostrate apices; slightly constricted on the keel side; keel puncta, 8 or 9 in 10 µ, extending as costÆ across the valve; striÆ delicate, 22 in 10 µ. L. 47 µ.

Brackish water, Long Island Sound.

Pl. 32, Fig. 21.

Grunowia

NITZSCHIA TABELLARIA GRUN.

Valve rhomboidal, inflated in the middle; apices produced; keel puncta extend in costÆ across half of the valve, 7 in 10 µ; striÆ transverse, about 22 in 10 µ. L. 20 µ.

Dimerogramma sinuatum Thwaites.

Nitzschia sinuata var. tabellaria (Grun.) V. H.

Schuylkill River. Not common.

Pl. 32, Fig. 7.

Scalares

NITZSCHIA SCALARIS (EHR.) WM. SM.

Valve linear, with obtusely conical apices; costÆ transverse, extending more or less to one-third the width of the valve, 3 or 4 in 10 µ; striÆ, 9 or 10 in 10 µ, punctate. Length of valve quite variable, up to 480 µ (Cleve).

A well-known form, abundant in salt marshes and more or less brackish water.

Pl. 33, Fig. 6. (To the right of the figure is an outline of the valve reduced one-third.)

Insignes

NITZSCHIA INSIGNIS GREG.

Valve nearly linear or linear-lanceolate; apices broad, slightly produced, obtuse; keel puncta extended into short costÆ, 4 or 5 in 10 µ; striÆ about 14 in 10 µ. Length variable up to 400 µ.

Delaware Bay.

Pl. 33, Fig. 8.

Bacillaria

NITZSCHIA PAXILLIFER (O. F. MUELLER) HEIBERG

Frustules united in a filament, afterwards free; valve lanceolate with nearly central keel; keel puncta, 7-9 in 10 µ; striÆ about 21 in 10 µ. L. 110 µ.

Vibrio paxillifer O. F. Mueller.

Bacillaria paradoxa Gmelin.

Nitzschia paradoxa (Gmelin) Grun.

Brackish water or streams subject to its influence.

Pl. 33, Figs. 13 and 14.

Otto Frederick Mueller, in 1786, published at Copenhagen a work on "Infusorial Animalcules," including a description of a Vibrio which he named paxillifer, obviously alluding to the partially-extended frustules bearing at the end a tablet-like bundle. Two years later, Gmelin described the same form as Bacillaria paradoxa, a name still used. Heiberg, however, in 1863, placed the form under Nitzschia where it properly belongs and called it Nitzschia paxillifer (O. F. Mueller). I have adopted Heiberg's name.

Perhaps the most remarkable of all diatoms. Many species possess the power of motion, which, however, is evident only in the free frustule. In N. paxillifer, the movement of the frustules occurs without the loss of continuity or adherence to each other, so that, while at one time the adnate frustules form a narrow filament, like that of Fragilaria, at another time they move laterally to their extreme length and form a thread of frustules adherent at their ends, later resuming their original position. The motion is repeated at intervals of from five to ten seconds. No satisfactory explanation of the movement has ever been made. In the filamentous form the frustules adhere to water-plants.

Vivaces

NITZSCHIA FLUMINENSIS GRUN.

Valve lanceolate, apices produced; keel puncta, 4-6 in 10 µ, partly extended in short costÆ; striÆ transverse, 14-15 in 10 µ, punctate; keel without a pseudo-nodule. L. 73 µ.

Common at Greenwich Point, Philadelphia.

Pl. 32, Fig. 16.

The form here figured is smaller than the type, which is from 130-160 µ in length.

SpathulatÆ

NITZSCHIA SPATHULATA BRÉB.

Frustule linear, truncate, dilated at the ends; zone with longitudinal folds; valve lanceolate, keel central; apices acute, with an elevated appendage; keel puncta, 5-6 in 10 µ; striÆ very fine. L. 56 µ.

Atlantic City and Cape May, N. J. (Lewis).

Pl. 40, Fig. 3.

DissipatÆ

NITZSCHIA DISSIPATA (KUETZ.) GRUN.

Valve lanceolate, with sub-rostrate apices; keel excentric; keel puncta about 6 in 10 µ; striÆ, 14 in 10 µ. L. 20-40 µ.

Fresh and brackish water.

Pl. 40, Fig. 7.

SigmoideÆ

NITZSCHIA MACILENTA GREG.

Frustule sigmoid, truncate at the ends; valve linear, with sub-acute apices and nearly central keel; keel with 5-6 puncta in 10 µ; striÆ obscure, about 25 to 28 (?) in 10 µ. Length variable, up to 490 µ.

As the valve is usually seen when the keel is on the margin, the outline (reduced one-third, shown to the left of the figure) is, as a rule, sigmoid.

Delaware Bay.

Pl. 33, Fig. 7.

NITZSCHIA VERMICULARIS (KUETZ.) HANTZSCH

Valve linear, sigmoid, attenuated toward the obtuse ends; keel puncta, 9 in 10 µ, quite distinct; striÆ very fine. L. 105 µ.

Fresh-water pools.

Pl. 32, Fig. 24; Pl. 33, Fig. 9.

SIGMATA

NITZSCHIA SIGMA (KUETZ.) WM. SM.

Frustule linear, sigmoid; valve linear, slightly sigmoid, tapering to the sub-acute apices; keel excentric, puncta, 8 in 10 µ; striÆ, 20-24 in 10 µ. L. to 250 µ.

Along the coast.

Pl. 39, Fig. 13.

NITZSCHIA SIGMATELLA GREG.

Valve linear, sigmoid, slightly attenuated toward the obtuse apices; keel excentric, puncta, 8-10 (?) in 10 µ; striÆ delicate, 25-30 in 10 µ. L. to 400 µ. The keel puncta are quite obscure.

Nitzschia curvula Wm. Sm.

Nitzschia sigma var. curvula (Wm. Sm.) De Toni.

Fresh water. Hammonton Pond; May's Landing, N. J.

Pl. 33, Figs. 4 and 5.

Gregory remarks that the keel puncta are seen in some specimens. In both of the forms figured I have counted 30 striÆ in 10 µ, but, after many examinations, I have not been quite certain about the keel puncta. The general appearance of the valves in any position is that of a Stenopterobia or Surirella anceps, with which it occurs.

NITZSCHIA CLAUSII HANTZSCH

Valve linear, slightly sigmoid, tapering to the sub-capitate ends; keel puncta, 11 in 10 µ; striÆ subtle. L. 40 µ.

Abundant in Ridley Creek, Delaware Co. (Palmer).

Pl. 32, Fig. 20.

ObtusÆ

NITZSCHIA OBTUSA WM. SM.

Frustule sigmoid, rounded at the ends; keel somewhat excentric, inflexed in the middle, the two median puncta distant; keel puncta, 5-6 in 10 µ; striÆ, 26 in 10 µ. L. to 300 µ.

Along the coast.

Pl. 39, Fig. 16.

NITZSCHIA OBTUSA VAR. FLEXELLA H. L. SMITH

Valve more attenuate at the ends than the type and smaller.

Pl. 39, Fig. 14.

NITZSCHIA OBTUSA VAR. SCALPELLIFORMIS GRUN.

Valve linear, with apices unilaterally truncate; keel excentric; keel puncta, 8 in 10 µ; striÆ, 26 in 10 µ. L. 48 µ.

Along the coast.

Pl. 32, Fig. 17.

Spectabiles

NITZSCHIA SPECTABILIS VAR. AMERICANA GRUN.

Frustule linear, slightly constricted in the middle, with sub-cuneate ends; valve linear, slightly arcuate, tapering to the sub-rostrate ends; keel excentric, keel puncta sometimes confluent, 4-6 in 10 µ, prolonged into short costÆ; striÆ distinct, 14 in the middle, 18 at the ends in 10 µ (but variable in different specimens). L. 186 µ.

Blue clay, especially at Tioga St.

Pl. 33, Fig. 3; Pl. 39, Fig. 1.

This is, probably, one of the most beautiful of the NitzschiÆ. It sometimes, according to De Toni, reaches a length of 520 µ.

Grunow states that his variety is found in the S. Bridgeton deposit. In a slide of Moeller labelled "Bridgeton, Maine," I find specimens identical in every respect with the Philadelphia form.

Lineares

NITZSCHIA LINEARIS (AG.) WM. SM.

Valve linear, slightly inflexed in the middle; keel excentric; keel puncta, 8-9 in 10 µ, the two median distant; striÆ about 30 in 10 µ. Frustules in zone view narrowed toward the ends, truncate. L. 75 µ.

Very common in fresh water.

Pl. 32, Fig. 18. Fig. 20, Pl. 40, a transverse section of frustule.

LanceolatÆ

NITZSCHIA PALEA (KUETZ.) WM. SM.

Valve linear-lanceolate, slightly rostrate at the apices; keel puncta, 10 in 10 µ, the median not distant; striÆ, 33-36 in 10 µ; zone view linear, with rounded ends. L. 25-65 µ.

Fresh water.

Pl. 32, Fig. 15.

NITZSCHIA AMPHIBIA GRUN.

Valve lanceolate, apices sometimes slightly produced, rounded; keel puncta, 8-9 in 10 µ; striÆ, 16 in 10 µ. L. 20-32 µ.

Fresh water.

Pl. 32, Figs. 14 and 25.

NITZSCHIA COMMUNIS RAB.

Frustule linear, slightly attenuated at the obtuse ends; valve elliptical-lanceolate, attenuated toward the obtuse ends; keel puncta, 12 in 10 µ; striÆ more than 30 in 10 µ. L. 35 µ.

Fresh water.

Pl. 32, Fig. 19.

NITZSCHIA INTERMEDIA HANTZSCH

Valve linear-lanceolate; keel puncta, 8 in 10 µ; striÆ about 24 in 10 µ. L. 100 µ.

Crum Creek. Not common.

Pl. 33, Fig. 2.

Nitzschiella

NITZSCHIA LONGISSIMA (BRÉB.) RALFS

Valve linear-lanceolate, with exceedingly long horns or beaks; keel puncta about 10 in 10 µ; striÆ about 16 in 10 µ. L. to 500 µ.

Shark River, N. J.

Pl. 33, Fig. 1.

Forma parva V. H.—Keel puncta, 10-12 in 10 µ. L. 70 µ.

East Park Reservoir, Philadelphia.

Pl. 33, Fig. 10.

Differs from N. closterium (Ehr.) Wm. Sm. in the keel puncta.

The type form occurs in brackish and salt water. The occurrence of the variety in fresh water is another instance of the finding of presumably brackish forms in the water supply of the city. If these cases prove to be unusual, it may be because of one of two reasons. The Schuylkill River, before the building of the dam at Fairmount, was tidal as far as the Falls of Schuylkill, and brackish influences, while not now existent, may have caused the growth of forms which now survive. Another reason may be that the opening of the locks at Fairmount Dam may cause a slight admission of brackish forms from tidal water below. The abundance of the brackish species appears to indicate that the first reason is the more plausible.

NITZSCHIA REVERSA WM. SM.

Valve lanceolate extended into beaks or horns curving in opposite directions; keel puncta not evident; striÆ, "20-26" in 10 µ. L. 70 µ.

Brackish water. Abundant in Duck Creek, Delaware River.

Pl. 33, Fig. 11.

NITZSCHIA ACICULARIS (KUETZ.) WM. SM.

Valve lanceolate, with beaks or horns about half the length of the median part of the valve; keel puncta, 18 in 10 µ; striÆ exceedingly delicate, "about 40 in 10 µ." L. 45 µ.

Fresh water. Darby Creek.

Pl. 33, Fig. 12.

Homoeocladia AG. (1827)

(homoios, like, and clados, a branch)

Frustules like Nitzschia, but enclosed in branching or simple tubes.

HOMŒOCLADIA FILIFORMIS WM. SM.

Frustule linear, tumid in the middle, obtuse at the ends; valve linear-lanceolate, with somewhat acute apices; keel central or nearly so; keel puncta, 8 in 10 µ; striÆ delicate. L. 108 µ.

Fresh and brackish water. Newark, N. J.

Pl. 33, Fig. 15.

(named after Dr. Suriray, a physician of Havre)

Valve linear, elliptical or ovate; pseudoraphe linear or lanceolate; a marginal keel forming wings or alÆ seen in zone view; costÆ short or reaching the pseudoraphe, frequently with intercostal striÆ more or less evident.

The genus is divided by Grunow according to the length and form of the costÆ. I include Stenopterobia.

Section 1.—CostÆ of nearly equal width throughout, reaching the pseudoraphe.

Section 2.—CostÆ short or marginal.

Section 3.—CostÆ dilated at the margin, attenuated toward the pseudoraphe.

Section 4.—Valve having the appearance of Nitzschia, with inconspicuous alÆ (Stenopterobia).

The endochrome consists of two laminate chromatophores, one on each valve.

The auxospores are single, originating from the union of two frustules (H. L. Smith).

Section 1

SURIRELLA BISERIATA (EHR.) BRÉB.

Valve lanceolate, subacute at the ends; costÆ robust, about 2 in 10 µ, parallel in the middle, radiate at the ends; pseudoraphe narrow. L. 100 µ.

Surirella bifrons Ehr.

Fresh water.

Pl. 39, Fig. 12; Pl. 35, Fig. 2 (smaller form).

SURIRELLA LINEARIS WM. SM.

Valve linear, with cuneate ends, slightly constricted in the middle; costÆ parallel, 2-3 in 10 µ. L. 90 µ.

Fresh water.

Pl. 35, Fig. 8.

SURIRELLA AMPHIOXYS WM. SM.

Valve oblong-linear, with cuneate ends; pseudoraphe narrow; costÆ, 3-4 in 10 µ; striÆ, 14-16 in 10 µ, somewhat radiate. L. 34-54 µ.

Surirella moelleriana Grun.

Fresh and brackish water. Common along the coast.

Pl. 35, Figs. 12 and 13.

SURIRELLA ROBUSTA EHR.

Valve linear-ovate; pseudoraphe wide; alÆ prominent; costÆ wide, 1¼ in 10 µ. Frustule in zone view clavate. L. 200-365 µ.

Fresh water.

Pl. 36, Fig. 2.

SURIRELLA SPLENDIDA (EHR.) KUETZ.

Valve ovate; costÆ, 1½ to 2 in 10 µ; pseudoraphe linear, narrow. L. 125-200 µ.

Fresh water.

Pl. 35, Fig. 3.

S. splendida is smaller than S. robusta and wider in proportion, but, as intermediate forms occur, it is difficult to distinguish between them.

SURIRELLA ELEGANS EHR.

Valve ovate, rounded at one end and acute at the other; pseudoraphe lanceolate, narrow; costÆ, 1½ in 10 µ; striÆ subtle, 22 in 10 µ. Frustule in zone view cuneate. L. 180-220 µ.

Fresh water.

Pl. 36, Fig. 1.

SURIRELLA STRIATULA TURPIN

Valve broad, obovate or elliptical, rounded at each end; costÆ, 1¼ in 10 µ, curved at the ends; striÆ, 14 in 10 µ. Frustule in zone view cuneate; marginal alÆ quite robust. L. 100-160 µ.

Blue clay. Brackish water.

Pl. 34, Fig. 1.

In the specimen figured, the outline is exactly elliptical, although the species is usually conical at one end.

SURIRELLA GEMMA EHR.

Valve ovate or ovate-elliptical, rounded at each end, sometimes asymmetrical along the longitudinal axis; pseudoraphe very narrow; costÆ distant, at irregular intervals, about 2 in 10 µ, somewhat radiate, reaching the pseudoraphe; striÆ, 20 in 10 µ, punctate. Frustule in zone view cuneate. L. 70-120 µ.

Along the coast.

Pl. 36, Fig. 4.

SURIRELLA TENERA GREG.

Valve ovate; pseudoraphe narrow, well-defined; costÆ indistinct, 2½ in 10 µ, their margins invisible; striÆ about 14 in 10 µ, punctate, more evident near the margin. L. 90 µ.

Surirella diaphana Bleisch.

Pavonia, N. J., artesian well.

Pl. 35, Fig. 6.

The figure is that of the var. nervosa A. S. (Atlas, Pl. 23, Fig. 15), which differs from the type in having the position of the costÆ indicated by scattered puncta.

Section 2

SURIRELLA GUATIMALENSIS EHR.

Valve ovate; pseudoraphe very narrow and indistinct; costÆ short, marginal, 2-2½ in 10 µ, absent from the rounded end. L. 120 µ.

Surirella cardinalis Kitton.

Smith's Island, Delaware River.

Pl. 36, Fig. 5.

SURIRELLA OVALIS BRÉB.

Valve ovate; costÆ short, marginal, radiate, 3-6 in 10 µ, often unequal; central area ovate, indistinctly costate; striÆ scarcely visible, about 18 in 10 µ; pseudoraphe narrow. L. 45-93 µ.

Surirella davidsonii A. S.

Fresh or brackish water.

Pl. 35, Fig. 5; Pl. 39, Fig. 11.

The smaller specimen is from the Delaware River, and the larger from the Hudson River.

SURIRELLA CRUMENA BRÉB.

Valve nearly orbicular; costÆ short, marginal, radiate; pseudoraphe narrow, indistinct; central area indistinctly costate, sometimes interrupted.

On account of the extreme confusion in the names of many forms which appear to be variations of S. ovalis, I have followed Van Heurck in retaining the original names as specific. De Toni gives S. crumena as a variety of S. ovalis.

Fresh and brackish water. Quite common in the Delaware River.

Pl. 35, Fig. 4.

SURIRELLA PINNATA WM. SM.

Valve ovate or oblong-ovate; costÆ reaching the linear pseudoraphe, about 6 in 10 µ. L. 40 µ.

Surirella ovalis var. pinnata (Wm. Sm.) De Toni.

S. pinnata is the type of a number of small forms usually found together, including S. panduriformis, S. angusta and S. minuta.

Fresh water. Media (Palmer).

Pl. 36, Fig. 7; Fig. 9 (abnormal).

Var. minuta, a small form of S. pinnata, occurs with the type.

SURIRELLA PANDURIFORMIS WM. SM.

Valve linear-oblong, with rounded ends, more or less constricted in the middle; otherwise as in S. pinnata. L. 54 µ.

Fresh water.

Pl. 36, Fig. 6.

SURIRELLA ANGUSTA KUETZ.

Valve linear, with cuneate ends; otherwise as in S. pinnata.

Fresh water.

Pl. 36, Fig. 8.

S. pinnata, S. panduriformis, and S. angusta have a narrow central area, and differ from S. ovalis which has short costÆ.

SURIRELLA OBLONGA EHR. ?

Valve elliptical-lanceolate, with obtuse ends; costÆ, marginal, 2½ in 10 µ; median area granulate; pseudoraphe narrow, lanceolate, scarcely visible; striÆ about 18 in 10 µ. L. 60 µ.

Blue clay. Rare.

Pl. 35, Fig. 9.

This has the outline and appearance of S. oblonga Ehr. (Mik. Pl. 15, Fig. 48), but the costÆ are closer.

SURIRELLA RECEDENS A. S.

Valve ovate; costÆ, 2-2½ in 10 µ; pseudoraphe narrow, not reaching the ends of the valve; intercostal spaces more evident near the middle. L. 50 µ.

Blue clay. Not uncommon.

Pl. 35, Fig. 7.

SURIRELLA CRUCIATA A. S.

Valve ovate; pseudoraphe very narrow; costÆ, 2 in 10 µ; the outline of several of the median costÆ strongly emphasized, while the other costÆ are indistinct. L. 54 µ.

Blue clay.

Pl. 35, Fig. 10.

SURIRELLA GRACILIS GRUN.

Valve linear, with sub-cuneate ends, slightly constricted in the middle; pseudoraphe very narrow; costÆ, 6-7 in 10 µ; transverse striÆ about 26 in 10 µ, punctate. L. 75 µ.

According to De Toni (p. 598), this form is a Nitzschia. It has, however, a narrow pseudoraphe.

Pavonia, N. J., artesian well. Rare.

Pl. 35, Fig. 11.

Section 3

SURIRELLA FASTUOSA EHR.

Valve ovate; costÆ about 1-2 in 10 µ, dilated at the margin and contracting at about one-fourth the distance toward the middle; area, ovate-lanceolate; pseudoraphe, narrow and indistinct; intercostate striÆ more evident near the margin, 19 in 10 µ, becoming again evident in a narrow band about one-half the distance to the pseudoraphe. L. 50-120 µ.

Along the coast. More common southward.

Pl. 35, Fig. 1.

SURIRELLA FEBIGERII LEWIS

Valve ovate-lanceolate; costÆ about 2½ in 10 µ with punctate interspaces extending half the distance toward the median hyaline area, which is divided longitudinally on each side of the narrow pseudoraphe by two longitudinal bands composed of short, transverse, irregular, punctate lines.

Along the coast.

Pl. 36, Fig. 3.

Section 4 (Stenopterobia)

SURIRELLA ANCEPS LEWIS

Frustule linear, straight or nearly so; valve sigmoid with rounded apices; costÆ marginal, nearly obsolete; striÆ distinct, about 15 in 10 µ; pseudoraphe wide. L. to 320 µ.

Hammonton Pond and Tom's River, N. J.

Pl. 34, Fig. 2.

SURIRELLA INTERMEDIA LEWIS

Frustule linear, straight, widened at the truncate ends; valve linear, sigmoid, tapering to the sub-acute ends; costÆ about 5 in 10 µ; striÆ about 20 in 10 µ. L. variable.

Hammonton Pond, N. J.

Pl. 34, Fig. 3; Pl. 39, Fig. 9 (zone view).

This, perhaps, is forma sub-acuta Fricke.

Fig. 7, Pl. 34, is probably a small form of S. intermedia, from Willistown, Pa. It resembles a Nitzschia.

SURIRELLA DELICATISSIMA LEWIS

Frustule linear, rounded at the ends; valve linear-lanceolate, sometimes very slightly constricted in the middle, with acute apices; costÆ, 5 in 10 µ; striÆ about 20 in 10 µ; pseudoraphe well defined, lanceolate. L. to 90 µ.

Fresh water. Newtown Square.

Pl. 34, Figs. 5 and 6 (small forms).

SURIRELLA ARCTISSIMA A. S.

Valve linear, tapering to the sub-acute ends; costÆ marginal, 5 in 10 µ; striÆ, 18 in 10 µ; pseudoraphe not evident. L. 184 µ.

May's Landing, N. J.

Pl. 34, Fig. 4.

Fig. 10, Pl. 39, is a small form from Newtown Square, Pa., in which the length is 86 µ, the costÆ 5 and the striÆ 16 in 10 µ.

Podocystis KUETZ. (1844)

(pous, a foot, and cystis, a bag)

Frustules cuneate, similar to Surirella, but attached by short stipes to other algÆ; valve obovate.

PODOCYSTIS ADRIATICA KUETZ.

Valve nearly symmetrical, obovate, with transverse costÆ about 4 in 10 µ, alternating with double rows of coarse puncta; median line distinct, linear. L. 43 µ.

Podocystis americana Bail.

Hell Gate, N. Y.

Pl. 40, Fig. 6.

Cymatopleura WM. SM. (1851)

(cuma, a wave, and pleura, a side)

Valve elliptical; surface transversely undulate, with short, marginal costÆ. Frustule in zone view linear, with undulated sides.

Auxospore formation as in Surirella.

CYMATOPLEURA SOLEA (BRÉB.) WM. SM.

Valve oblong, with cuneate apices, constricted in the middle; costÆ about 6 in 10 µ; striÆ, 10 in 10 µ; pseudoraphe scarcely visible. L. 50-300 µ.

Blue clay. Common in the Hudson River.

Pl. 34, Figs. 8 and 9.

CYMATOPLEURA ELLIPTICA (BRÉB.) WM. SM.

Valve elliptical; marginal costÆ short, 3 in 10 µ; striÆ delicate, 18 in 10 µ; undulations four or more. L. 70-140 µ.

Blue clay.

Pl. 37, Fig. 1.

Forma spiralis.—Valve ovate, swelled into curved ridges at the lower end, with a contraction of the valve.

Port Penn, Delaware River.

Pl. 37, Fig. 2.

CYMATOPLEURA MARINA LEWIS

Frustule linear, with numerous undulations, ends apiculate; valve linear-lanceolate, with acute ends; striÆ transverse, punctate at unequal intervals, from 16-18 in 10 µ. L. 43 µ.

East River, N. Y.

Pl. 37, Figs. 3 and 4.

Lewis states that the ends are more or less truncate. I do not find them so.

Campylodiscus EHR. (1841)

(campulos, curved like a saddle)

Valve orbicular or sub-orbicular, with costÆ or punctate rays converging from the circumference toward the hyaline centre, which sometimes appears like a pseudoraphe. Frustule of two saddle-shaped valves at right angles to each other. The zone view may be of almost any shape according to position.

Endochrome consists of two bands, each lining the inner surface of each valve. Auxospore and conjugation unknown.

CAMPYLODISCUS ECHENEIS EHR.

Valve sub-orbicular, saddle-shaped; costÆ indistinct, short, marginal; rows of round or elongated puncta converge toward the lanceolate, hyaline median space. Diam. 80-140 µ.

Campylodiscus argus Bail.

Blue clay. Reservoir at Thompson and Twenty-sixth Sts., Phila.

Pl. 37, Fig. 6.

This form, usually considered as brackish and marine, is occasionally found in fresh water. According to Deby, it is fossil in the "Champlain deposit of N. A."

CAMPYLODISCUS HIBERNICUS EHR.

Valve irregularly orbicular; costÆ, 40-60, about 2 in 10 µ, wide at the margin and attenuated toward the centre which is somewhat quadrate; the radials rough with minute apiculi.

Pensauken, N. J., artesian well.

Pl. 37, Fig. 5.

APPENDIX

Collection and Preparation of Diatoms

It is assumed that every student of the DiatomaceÆ has a general knowledge of the collection, preparation, mounting and examination of material. For the novice, however, the following methods, used by the author for many years, may be of service.

Collection of Fresh-water Material.—The yellow film on the inside of aquaria always contains small species. Stems of water-plants near the shores of ponds and the submerged roots, the brownish coating of rocks in streams and water-falls, fountains, and water-troughs, are prolific. At all times of the year, some diatoms may be found in a thin layer upon the mud of rivers or creeks. In the spring, brown patches of mud, filled with bubbles, floating near the shore in ponds, or coming down with the current in rivers, are rich in various forms. Within the limits assigned to our district, I have made collections in the following localities: Schuylkill River, including the region near Fairmount Dam, several reservoirs and the water-supply; the Wissahickon and Fairmount Park, Darby, Crum and Ridley Creeks, the Neshaminy and the Brandywine; meadow pools and rivulets near the city; the upper Delaware, the Water Gap and numerous cascades northward; the Shawangunk Mountains and the Poconos; many parts of New Jersey along the coast; the Pine Barren region, the Hammonton, Atsion and Kirkwood Ponds and the swamps near Atco.

In the collection of fresh-water material, it is well to be provided with a number of small bottles. Take a handful of the water-plants or algÆ, and squeeze the material into the bottles, or, lacking a bottle, wrap it in paper. With a small forceps it is possible to detach minute quantities of a pure gathering which may not need further preparation beyond burning to a red heat on the cover-glass before mounting. A malacca cane, with extending rod to which may be screwed a bottle, net, spoon or hook, is useful on a long trip. If it is impossible to separate the thin film of diatoms from the mud in the bed of streams, dip up the surface mud with one bottle, allow to settle a few minutes, then pour off the supernatant liquid, which will be comparatively free from sand, into another bottle. It must be confessed, however, that the mud in streams near Philadelphia contains a large quantity of fine mica which, in some instances, it is impossible to remove.

Collection of Marine Material.—Shell scrapings, the stomachs of fish, marine algÆ, especially the brown and red algÆ, the hulls of vessels, mud from anchors and dredgings, are all sources which may prove valuable. In the sand ripples, after the tide recedes, a yellowish-brown deposit will be noticed. This should be taken up carefully with a spoon and placed in a bottle; the sand will settle at once and a very pure gathering will be held in suspension in the water. Such collections may be made along the entire coast of New Jersey on sunny days in summer. In salt meadows near Absecon and Hackensack, large quantities of diatoms, including Pleurosigma, may be obtained in the yellow scum floating on the surface.

The Blue Clay Deposit.—The blue clay occurs as a pre- or post-glacial deposit in the bed of the ancient Delaware River, and, at depths varying usually from fifteen to forty feet below the surface, has been obtained from artesian wells at Pavonia, Pensauken and Gloucester, N. J., also at Port Penn on the Delaware, and especially from the dredgings made by the removal of Smith's Island opposite the city. In the city proper, it may be stated briefly that material may be found in a stratum of very light blue clay at a depth varying from twenty to sixty feet in many places south of Arch St. east of Broad St., and also along the beds of ancient rivulets near Tioga St., at Sixteenth St., and in certain other places which were probably subject to tidal overflow. One of the best collections was made along the bank of the Schuylkill at the east end of Walnut St. Bridge, at a depth of thirteen feet below the surface. Excavations for the Reading Terminal and the Subway and several buildings, as the Bingham House, have furnished numerous specimens.

Cleaning the Material.—Some gatherings may be so pure as to be ready for mounting when treated with dilute alcohol and oil of cloves. If, when gathered, the diatoms are immersed in a saturated solution of picric acid for several days, they may be stained with carmine or methylene blue, or whatever may be required to emphasize the contents of the frustules, including the endochrome and the pyrenoids. After staining, pass as rapidly as expedient through the treatment with dilute alcohol and oil of cloves, and mount in benzol balsam, avoiding heat. A hot solution of mercuric bichloride is sometimes used for the preservation of the endochrome, although washing is needed before mounting. For the particular stain considered best for certain details of structure, it will be advisable to consult works on Micro-Chemistry or Heinzerling (l. c.). The stains of most importance are carmine, methylene blue, hÆmatoxylin, gold chloride and Bismarck brown.

Whatever method may be used in staining, the identification of forms is impossible, in most cases, unless the valves are carefully cleaned and the cell-contents destroyed. For this purpose provide a casserole holding from five to eight ounces, an iron tripod stand with alcohol lamp, several six-inch test-tubes, preferably those with a standard base, fitted with pure rubber corks. Take the material as free from twigs, dead leaves, sand, and other matter as possible, place it in the casserole, and add about the same quantity of nitric acid. Boil for twenty minutes and then add about half a teaspoonful of powdered bichromate of potash, stirring with a glass rod. Then take a beaker-glass partly filled with water and pour into it slowly the liquid which has been allowed to cool a short time, whirling the casserole to cause the concentration of sand in the centre. Allow the material to settle for half an hour or longer, according to the amount of diatoms and their size. Pour off the water, add more water, and place in a test-tube. Repeat the decantation, shaking the test-tube, closed with a rubber cork, vigorously each time. From time to time whirl the diatoms in the casserole and throw away the sand collected in the centre. By repeating the decantation, shaking and whirling, the deposit will be found to consist almost entirely of diatoms. It may be necessary to repeat the boiling in the acid and bichromate. If, however, any detritus other than sand is noted, boil in sulphuric acid and add from time to time minute pinches of powdered chlorate of potash, being careful to protect the eyes by holding a piece of glass before them; otherwise the explosions which occur are likely to throw some of the boiling acid into the eyes and destroy the sight. The material, when clean, should be white or, in the case of Synedra, yellowish. It is quite easy to construct a box fitted with the proper apparatus for boiling and provided with a glass door for observation, and a method of introducing the chlorate of potash through a small aperture or tube. The box may be placed in the garden or fastened outside of a window so that the poisonous fumes may be carried off.

An excellent method, in the case of larger forms, is to boil the material already cleaned by the acid in water to which a few shavings of coarse brown soap are added. The difference in density will hold in suspension any flocculent matter, and while many of the smaller forms will not settle, the others will be perfectly cleaned. When satisfied with the cleaning, preserve the stock material in part alcohol and, in using, pour into a smaller bottle the amount required, replace the dilute alcohol with distilled water, and mount as directed. It often happens that gatherings are made consisting almost entirely of sand. Attempts at cleaning in the usual way will cause the loss of nearly all of the diatoms. In this case, after the material has been treated with acid until nothing remains but sand and a few diatoms, the mechanical finger must be used.

In the cleaning of marine deposits, various methods may be required. In the case of partly siliceous species, washing in pure water repeatedly is all that can be done. The larger and heavier diatoms may be separated from the sand by elutriation or by whirling in a casserole, by rocking in a shallow dish the shape of a watch crystal, or by pouring slowly over a strip of plate-glass at least two feet in length inclined at an angle of thirty degrees. The sand will cling to the glass, while the greater portion of the diatoms will run off. Where particles of shells or foraminifera are present, a preliminary boiling in hydrochloric acid is advisable. In all marine gatherings, the salt should first be washed out before proceeding with the cleaning.

For hardened masses of clay and for fossil deposits, it is necessary to boil in carbonate of soda and follow with the acid treatment. Citric acid and acetate of potash used alternately in boiling may be tried. Soaking for a time in acetate of potash and allowing the material to deliquesce for a week before further process, has proved successful in some instances. The repetition of several methods and the gentle breaking of the harder masses with the point of a needle will disintegrate almost any diatomaceous earth, but, as a last resort for refractory deposits, boil in pure water, add a piece of caustic potash about the size of a pea, continue the boiling not more than thirty seconds longer, and pour instantly into dilute hydrochloric acid; otherwise the diatoms will be destroyed. Afterwards proceed with the usual treatment.

Slides and Covers.—Take half an ounce of No. 1 covers, circles, and place them in a wide-mouthed bottle. Add a portion of the following mixture (Dr. Carl Seiler's formula):

Bichromate of potash	2 oz.
Sulphuric acid	3 fl. oz.
Water	25 fl. oz.

Shake the bottle in order that the surfaces of the covers may be fully exposed to the action of the acid, and set aside for several hours. Decant the solution, add water repeatedly until all traces of the mixture are removed, and keep the circles in the bottle in fifty-per cent. alcohol. When needed, take out a circle with forceps and dry on a linen cloth.

The slides may be treated in the same way, or they may be easily prepared by immersion in a solution of washing soda, and then washed and dried. This process may be used in cleaning the balsam or styrax from old slides.

Preparation of Strewn Mounts.—Place several covers on the mounting stand. With a dipping tube, cover each circle with distilled water, and add a small drop of the prepared diatoms, being careful to avoid any vibration of the stand. Heat the stand until small bubbles begin to appear, remove the lamp, and allow the water to evaporate. If the above method is carefully followed, the diatoms will be deposited in an even layer, provided the material is not too dense. Take a slide, centre it, and place a small amount of styrax on the centre. Invert the prepared cover, and gently place it upon the styrax. Heat the slide on the mounting stand until the styrax bubbles and then allow to cool. If bubbles still remain, heat again until they disappear. It is well to mount several slides more than required, as some may be imperfect.

Preparation of Selected Mounts.—Take a slide, place a minute quantity of beeswax on two places at a distance apart nearly equal to the diameter of the cover used. Place a cover on the wax and press it down flat, or sufficiently to keep it in position. Dip a fine needle into the following cement:

Glacial acetic acid	12 drachms
Gelatine	02 drachms
Alcohol	01 drachm

This is made by adding the acid to the gelatine in a water-bath and then the alcohol, and filtering. Apply the moistened needle to the centre of the cover and spread as small a quantity as possible in a thin layer. Now place the slide upon the turn table, centre it with respect to the position of the gelatine, and with the finest sable brush draw a circle about a tenth of an inch in diameter around the gelatine in water-color (Windsor), blue or vermilion, or in India ink. Instead of the water-color, a circle of tin-foil the size of the cover and pierced with a hole in the centre may be used, but the colored circle is to be preferred, as, when brought into view, it indicates exactly the focus required for observing the diatom.

The bottle containing the cleaned material, which has been kept in water and alcohol, should be refilled with distilled water and well shaken, when a small portion may be taken up with a dipping tube and evenly distributed over a portion of a slide and then dried. By the use of a mechanical finger, fitted with a small piece of finely spun glass attached by wax to the holder of the finger, when the microscope is focussed until the glass thread touches the diatom selected, it will adhere to the thread. Raise the body of the microscope, remove the slide containing the spread material, or move it to another part of the stage, and place the slide with the prepared cover in the same position. Now carefully lower the body-tube of the instrument until the diatom rests upon the gelatine, breathe gently upon it, remove the cover from the slide, invert it over another slide containing a drop of styrax and proceed by heating to mount as before. The size of the diatom, the amount of gelatine, and several other factors, will enter into the question of success or failure. I have, however, employed the above method and have mounted thousands of slides of selected diatoms successfully. It is necessary to avoid any air current which will cause the diatom to fall from the thread. On very cold days the glass thread sometimes becomes electrified and the diatoms will not stick; on sultry days in August in our locality the diatoms will stick too closely.

By the same method, slides of arranged diatoms can be made using a glass circle properly marked with lines in the eye-piece. Care should be taken to use glass threads more or less in proportion to the size of the diatoms. A cat's whisker is preferred by some to the glass thread. It has the advantage of not breaking, but unless it is quite short it is too flexible. If the point of the thread becomes covered with gelatine, lower it into a minute drop of water upon a separate slide, and by moving it about it will be cleaned. The diatom itself may be washed in the same way, if it is not too small.

Instruments Required.—For collecting, in order to determine the quality of the find, any simple lens of fifteen to twenty diameters is sufficient. A Stanhope is quite useful although difficult to obtain, while an achromatic triplet of sufficient power will probably be all that is necessary. For selecting with the mechanical finger, an objective of two-thirds-inch focus is the most convenient, but for determining species a one-fifth-inch is needed, an immersion objective being essential for minute forms.

No particular form of microscope is required. Any instrument having standard parts, inclination of the body to the axis, a sub-stage condenser and movable stage, will prove serviceable in nearly all investigations. For critical work, measurement of striÆ and location of specimens on the slide, the large models of Bausch and Lomb leave nothing to be desired. One smaller instrument may be used for rapid examination and for selection with the mechanical finger. If the stage is supplied with a vernier, the diatoms can be located rapidly and recorded for future reference. The Zentmayer Army Hospital stand with mechanical stage is excellent. The Continental stands, convenient for laboratory work, especially in the examination of bacteria, are not so serviceable as the larger stands of American and English make. The stand especially designed by Dr. Henri Van Heurck, the celebrated Belgian naturalist, is, without doubt, admirably suited to the investigation of the DiatomaceÆ. In the form of the Circuit Stage as made by Watson and Sons, of London, supplied with proper condenser and mechanical stage with vernier attachment, it has been used in the preparation of the present work with much satisfaction.

The drawings have all been made with an AbbÉ camera lucida, a 3 mm. objective and a No. 10 eye-piece, producing a magnification of about 800 diameters. All illustrations are from actual specimens in my cabinet or, in a few instances, from slides sent me by friends. In the measurement of striÆ and puncta, the number in ten microns is stated, and will be found to be approximately correct in most of the drawings, except when the number is in excess of twenty in ten microns, in which case it is impossible to represent the markings accurately on figures of the magnification adopted. All drawings are from specimens in this locality, except in a few cases mentioned in the text.

INDEX

(SYNONYMS IN ITALICS)

Caloneis,