  DEFINITION OF THE CLASS AMPHIBIA LINNÉ, 1758, DEVONIAN TO RECENT. (World-wide distribution.) Cold-blooded vertebrates; aquatic or partially terrestrial in habit; body scaled or naked or partly covered with bony or horny plates; abdomen sometimes protected by closely packed scutes, scales, or rods; skull completely roofed-over or with a single vacuity; pterygoid-palatine arch complete or wanting; stapes always present; two occipital condyles, sometimes cartilaginous; skull bones pitted and grooved by the lateral-line canals, or smooth and lateral-line canals wanting; parasphenoid well developed; palatine vacuities, large, small, or absent; basioccipital partly or entirely cartilaginous; sclerotic plates present or absent; mouth always terminal; teeth sharply conical, smooth, or plicated, with walls sometimes extremely complicated by the infolding of the dentine and enamel. VertebrÆ procoelous, opisthocoelous, amphicoelous, amphiplatyan, temnospondylous, stereospondylous, or cartilaginous; notochord often persistent; column divisible into cervical, dorsal, and caudal series; cervical series, so far as known, always short; dorsal region long or short; a single sacral or two; caudal series short, very long, or absent. Pectoral girdle composed of an osseous scapula, cleithrum, clavicle, interclavicle, and coracoid with various relations; sternum undeveloped; pectoral girdle of membrane bones; in Triassic forms producing the effect of a plastron on account of the high development of the clavicles and interclavicle. Pelvis usually composed of an osseous ilium and ischium; pubis when osseous surrounded by large amounts of cartilage, usually cartilaginous, sometimes calcified. Limbs ambulatory, natatory, or wanting; limb bones composed either entirely of perichondrium or of perichondrium and a small amount of endochondrium; radius and ulna, and tibia and fibula free or fused. Digits 3 to 5, usually 4 for the hand and 5 for the foot. Terminal phalanges sometimes clawed. Carpus and tarsus osseous or cartilaginous, usually the latter. Ribs never attached to a sternal apparatus, single or double headed or intermediate, long and curved or short and straight. Articulation with vertebral column inter- or intra-central. Respiration both branchial and pulmonary; branchiÆ persistent and osseous in some forms. Development by metamorphosis either in the egg membrane, on the back of the mother, or in the water. No amnion or allantois. Heart with a single ventricle and 3 or 4 pairs of aortic arches; postcava always present in the recent forms. DEFINITION OF SUBCLASS EUAMPHIBIA, MOODIE, 1909. COAL MEASURES TO RECENT. (World-wide distribution.) Moodie, Trans. Kans. Acad. Sci., 1909, p. 243. Moodie, Geol. Mag., n. s., Dec. V, vol. VI, p. 220, May, 1909. The present group was established for the reception of the Branchiosauria and their descendants, the Caudata, with the related forms, the Apoda. The Salientia are included provisionally, since there is no evidence of the origin or relationship of this group of animals to other Euamphibia save that they have attained the same stage of evolution. They are in no way closely related to any known group of Amphibia, recent or extinct, but they stand on the same plane of development as the Caudata and present similar structures, i.e., a single ventricle in the heart, external branchiÆ in the young, a glandular skin, perichondral bone, and a large parasphenoid. The origin of the Salientia is a puzzle and must remain so until further paleontological evidence is forthcoming. Wyman, Cope, and the writer have all remarked on the similarity of structure between the Salientia and the single known specimen of Pelion lyelli Wyman from the Linton, Ohio, Coal Measures. The subclass Euamphibia may be defined as follows: Aquatic or terrestrial Amphibia; development by metamorphosis; external branchiÆ present in the young; bones almost entirely perichondral; carpus and tarsus never ossified; osseous pubis absent; vertebrÆ usually amphicoelous with persistent notochord; ribs short and straight or flat and slightly curved, or absent; digits 4 in the hand and 5 in the foot; skull never grooved or pitted, nor cut by the lateral-line canals; lateral-line organs present in the skin; sclerotic plates present or absent; tail long and flattened or absent. Ribs in Triton walthi are secondarily long and curved. DEFINITION OF THE ORDER BRANCHIOSAURIA LYDEKKER, 1890. COAL MEASURES AND PERMIAN OF NORTH AMERICA AND EUROPE. Lydekker, Cat. Fossil Reptilia and Amphibia, pt. IV, p. 208, 1890. Extinct, salamander-like amphibians, with broad, obtusely rounded cranium; external branchiÆ present in young; sclerotic plates present; bones of the cranium not ornamented with deep pits and grooves nor cut by the lateral-line canals, though sometimes ornamented with slight scorbiculations; notochord always persistent; vertebrÆ cartilaginous (in caudal region) or but partially ossified, the ossification being entirely perichondral; a single sacral vertebra; transverse process of vertebrÆ large in dorsal region; ribs always short, straight, and heavy, present throughout the length of the vertebral column and borne on the transverse processes centrally; caudal region of moderate length with elongate fleshy tail; usually 20 presacrals, of which 4 or 5 may be considered cervicals; limbs natatory and always present, well developed; elements of the appendicular skeleton composed entirely of perichondrium; carpus and tarsus cartilaginous; digits 4 in the hand and 5 in the foot; phalangeal formula for the hand usually 2-2-3-2 and for the foot 2-3-4-3-2; distal phalanges not clawed; abdomen covered with closely packed corneous scutes or scales; body naked or covered with minute horny scales; median and dorsal lateral lines present on the posterior part of body and on tail. |
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