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 procœlous, opisthocœlous, amphicœlous, 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 amphicœlous 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.