62 THE EXTINCT BATRACHIA, REPTILIA 



No facial foramen ; muzzle long slender. 



HOLOPS. 



aa The cervical vertebra? with long simple zygapophyses. 

 Muzzle long narrow, with long symphysis ; teeth very unequal. 



THECACHAMPSA. 



Muzzle broad short, symphysis short. 



PLERODON. 



AA Teeth crowns a single dentinal cone with enamel sheath. 

 Cervical hypapophyses rudimental ; muzzle broad. 



BOTTOSAURUS* 



Cervical hypapophyses elongate, simple. 



EXISTING CROCODILIA. 



Species of this order have been abundant in North America from the beginning of the 

 Cretaceous period to the end of the Miocene. At present they are confined to its extreme 

 southern regions. 



The Cretaceous period was more prolific in them than any later one, for then the 

 Reptilian type in all its representatives reached its fullest development in the numbers, 

 variety and size of its members. Then our sea coasts, estuaries, and fresh waters 

 swarmed with them, an indication of the prolific lesser life on which they preyed or 

 otherwise vented their powers of destruction. 



THECACHAMPSA, Cope. 

 Proceedings Academy Natural Sciences, 1867, p. 143. 



This genus was characterized from a few teeth from the Miocene of Maryland. 

 Since then additional material has enabled me to construct its characters more fully. 



Muzzle elongate, slender, as in Gavialis, the symphysis of the mandible elongate ; den- 

 tal series interrupted by larger canine-like teeth. Dentine of the crown arranged in 

 concentric cones. Enamel thin, with a delicate anterior and posterior cutting ridge near 

 the tip of the crown. Cervical hypapophyses elongate, simple. 



The concentric structure of the dentine in this genus is quite the same as in Thora- 

 cosaurus. I do not discover in it sections of the teeth of Gavialis, Mecistops and Croco- 

 dilus. The cones readily separate and fall out in the fossil specimens. Their existence 

 would indicate a periodical cessation of activity in the secretory vessels on the wall of the 

 pulp cavity of the teeth, with intervening increase of deposit of dentine. In a shed tooth 

 of this genus four such cones may be counted.f 



*Probably the thin crown in this genus is composed of several attenuated cones. 



\k. supposed affinity of this genus to Mosasaurus, which I inserted in the original description, at the suggestion of 

 a friend, I do not now recognize. 



