Page:Synopsis of the Exinct Batrachia and Reptilia of North America. Part 1..pdf/68

 62 THE EXTINCT BATRACHIA, .REPTILIA No facial foramen ; muzzle long slender. IIOLOPS. ca The cervical vertebrae 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. Ger\ ical hypapophyses rudimental ; muzzle broad. Cervical hypapophyses elongate, simple. I3OTTOSAURCTS.* 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 NI ith them, an indication of the prolific lesser life ou which they preyed or otherwise vented their powers of destruction. THECA CHAMPSAI 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 Gm inns, 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. Ccivical 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.t *Probably the thin crown in this genus is eomposed of several attenuated cones. tA 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.