  Illustrated: Jaekel, Zeits. d. d. geol. Gesell., 1901, vol. 53, part 1, pls. 4, 5. Jaekel has described a specimen of this species obtained from the Middle Cambrian near Tejrovic, Bohemia, which on development showed beneath the test of the axial lobe, certain structures which he believed represented the casts of proximal segments of appendages. On the basis of this specimen he produced a new restoration of the ventral surface of the trilobite, in which he showed three short wide segments in the place occupied by the coxopodite of an appendage of Triarthrus. He also made the mouth parts considerably different from those of the latter genus. Beecher (1902) showed that the structures which Jaekel took for segments of appendages were really the fillings between stiffening plates of chitin on the ventral membrane, and demonstrated the fact that similar structures existed in Triarthrus. It cannot be said, therefore, that any appendages are really known in Ptychoparia striata, but some knowledge of the internal anatomy of the species is supplied by the specimen. Illustrated: Walcott, Smithson. Misc. Coll., vol. 57, 1912, p. 192, pl. 24, fig. 2;—Ibid., vol. 67, 1918, pl. 21, figs. 3-5 (corrected figure). Walcott has figured a single individual of this species showing appendages, the accompanying description being as follows (1918, p. 144): Ventral appendages. Only one specimen has been found showing the thoracic limbs. This indicates very clearly the general character of the exopodite and that it is situated above the endopodite, although there are only imperfect traces of the latter…. The exopodites are unlike those of any trilobite now known. They are long, rather broad lobes extending from the line of the union of the mesosternites and the pleurosternites. At the proximal end they appear to be as wide as the axial lobe of each segment, and to increase in width and slightly overlap each other nearly out to the distal extremity…. They are finely crenulated along both the anterior and dorsal margins, which indicates the presence of fine setÆ. The specimen is quite imperfectly preserved, but seems to indicate that the exopodite of Ptychoparia had a long, rather narrow unsegmented shaft. Measurements (from Walcott's figure): The specimen is a small one, about 9.5 mm. long, an individual exopodite is about 2 mm. long and the shaft 0.33 mm. wide. Horizon and locality: Middle Cambrian, Burgess shale, between Mount Field and Wapta Peak, above Field, British Columbia. Illustrated: Walcott, Smithson. Misc. Coll., vol. 67, 1918, p. 145, pl. 21, figs. 1, 2. Walcott figured one individual of this species showing long slender antennules projecting in front of the cephalon. It is of especial interest because one of the antennules shows almost exactly the same sigmoid curvature which is so characteristic of the related Triarthrus. The individual segments are not visible. Measurements: The specimen is 23 mm. long and the direct distance from the front of the head to the anterior end of the more perfect antennule is 9.5 mm. Measured along the curvature, the same antennule is about 11 mm. long. Horizon and locality: Same as the preceding. |
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