132 BATRACHIA. 



cannot be distinguished from the system of " abdominal ribs " 

 so conspiciious in many reptiles. 



Keraterpeton. A genus with comparatively large species, sometimes 

 as much as half a metre in length. The tail is much elongated, three 

 times as long as the trunk in the type species. The large orbits are far 

 forwards, and the cranium itself extends backwards considerably beyond 

 the cheeks. Its most singular feature consists in the large pair of pointed 

 horns, of undetermined nature, firmly fixed to the postero-lateral angles 

 of the cranium and directed backwards. The external bones are 

 sculptured. There are about 20 presacral vertebrae, and the thoracic 

 ribs are distinctly double-headed. The neural and haemal arches in the 

 caudal vertebrae are firmly fused with the centra, while their spines are 

 expanded and curiously pectinated at the truncate end. The limbs are 

 nearly equal in size, with unossified carpus and tarsus. The phalangeal 

 formula of the hind foot, which has five digits, is clearly proved to be 

 2, 3, 4, 4, 3. The scutes of the ventral shield are very small, and there 

 appears to have been no dorsal armour. The typical species, K. galvani, 

 occurs in the Coal Measures of Kilkenny, Ireland, and Staffordshire, 

 England, and probably does not exceed 0'3 m. in length. There is 

 evidence of allied species in the Coal Measures of Linton, Ohio, U.S.A. ; 

 and other forms, probably generically distinct, with rnoveable horns 

 ("epiotic cornua") and ossified carpal and tarsal elements, are known 

 from the Lower Permian of Bohemia. 



Sub-Order 4. Labyrinthodontia. 



It is remarkable that the large Stegocephalia with complex 

 teeth occur among the earliest as also among the latest known 

 representatives of the Order. There is little or no evidence of 

 evolution among them, except that the largest in size and those 

 most completely " labyrinthodont " are the latest in the series. 



The earliest of the Labyrinthodonts proper, however, from 

 the Lower Carboniferous of Scotland, are very imperfectly 

 known. It is particularly unfortunate that no satisfactory 

 remains of the limbs have hitherto been discovered. One 

 fragment of skull belongs to the genus Loxomma, better known 

 by skulls from the Coal Measures (Upper Carboniferous) of 

 England. Another unique fossil (named Pholidogaster pisci- 

 formis) represents a species more than a metre in length, with 

 the characteristic pectoral plates, ventral armour of oat-shaped 

 scutes, and an apparently rhachitomous vertebral axis. 



