PTERODACTYLUS. 273 



ISCHYRODON. 



1 17. The teeth of the Ischyrodon, a gigantic reptile from the Jura 

 limestone of the Canton of Aargau, somewhat resemble those of the 

 Thaumatosaurus, but the external longitudinal strise of the crown of 

 the tooth are sharper and more elevated, and between the striae 

 the enamel is roughened by irregular linear risings. 



PCECILOPLEURON. 



118. The teeth of the Pcecilopleuron (Deslongchamps), a gigantic 

 reptile whose remains occur in the oolitic beds at Caen, according to 

 the single tooth referred to that genus, has a more compressed 

 crown than the teeth of the Thaumatosaurus ; the strise are also wider 

 apart, and the two diametral ones are developed into ridges which 

 extend to the apex of the tooth. 



PTERODACTVLUS. 



119. The true affinities of this the most extraordinary of all the 

 ancient animals which Comparative Anatomy has brought to light, 

 were, when much conjElicting evidence was apparently given by other 

 parts, pointed out most distinctly by the dental system. Cuvier, 

 after discussing the various opinions w^hich had been promulgated 

 respecting the nature of the remains of the extinct volant animal in 

 question, says : — " The teeth, by which the examination of an animal 

 ought always to be commenced, here present nothing equivocal. 

 They are all simple, conical and nearly alike, as in the crocodiles, the 

 monitors and other lizards. "(1) Their disposition in the jaws with wide 

 interspaces, and their separate implantation in distinct sockets are cha- 

 racters in which the Pterodactyle approximates to the extinct Saurian 

 genera, Thecodon, Megalosaurus, Plesiosaurus, and the Crocodilians. 



In the Pierodactylus longirostris the teeth are of moderate and 

 equal size, slender, conical, sharp-pointed, recurved, with pretty 



(1) " Les dents, par ou il faut toujours commencer rexamen d'un animal, ne presentent ici 

 aucune equivoque. Elles sont toutes simples, coniques, et a peu pres semblables entre elles 

 comme dans les crocodiles, les monitors et d'autres lezards." Cuvier adds, " Tout le monde 

 sait que les dauphins seuls, parmi les mammiferes, pourraient presenter quelque chose de com- 

 parable." — Ossem. foss. Ed. 1836, torn, x, p. 225. 



T 



