50 THE COAL MEASURES AMPHIBIA OF NORTH AMERICA. 



The subclass Euamphibia may be defined as follows: Aquatic or terrestrial 

 Amphibia; development by metamorphosis; external branchiae present in the young; 

 bones almost entirely perichondral ; carpus and tarsus never ossified ; osseous pubis 

 absent; vertebrae usually amphiccelous 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 Rcptilia and Amphibia, pt. iv, p. 208, 1890. 



Extinct, salamander-like amphibians, with broad, obtusely rounded cranium; 

 external branchiae 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; 

 vertebrae cartilaginous (in caudal region) or but partially ossified, the ossification 

 being entirely perichondral; a single sacral vertebra; transverse process of vertebrae 

 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 peri- 

 chondrium; 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 homy scales ; median and dorsal lateral 

 lines present on the posterior part of body and on tail. 



