CROCODILIANS. 291 



and better defined ridges, two of which, on opposite sides of the 

 crown, are larger and more elevated than the rest. The fang is 

 smooth, cyhndrical, and always excavated at the base. The teeth of 

 the Steneosauri, or extinct Crocodiles with long and slender jaws 

 and with vertebree subconcave at both extremities, but with sub- 

 terminal nostrils, differ from those of the Teleosauri in being some- 

 what thicker in proportion to their length, and larger in propor- 

 tion to the jaws. 



A distinct genus of extinct Crocodile (Marmarosaurus) is indicated 

 by a form of tooth differing from that of the Steneosaurus in being sub- 

 compressed, and in having the ridges on the basal two-thirds of the 

 crown shorter, more frequently interrupted, irregularly alternating, 

 and slightly wavy ; the two opposite stronger ridges are not deve- 

 loped. Teeth of this kind, with crowns fifteen lines in length, and 

 six lines across the long diameter of the base, occur in the Forest- 

 marble, PL 75 a, fig. 5. 



A more remarkable and almost heart-shaped form of tooth, 

 is presented by the extinct Crocodilian genus denominated, from 

 this character, Cardiodon. The crown of the tooth suddenly ex- 

 pands above the neck, as in the Caiman, but is more flattened 

 transversely and is broader antero-posteriorly, terminating in an 

 edge before and behind, and contracting to a point above, which 

 is generally more or less abraded. The enamel is roughened by wavy 

 longitudinal ridges, with more minute rugse in their interspaces. 

 The fang of the tooth is smooth and cylindrical, PI. 75 a, fig. 7.(1) 



Structure. — The teeth of both the existing and extinct Croco- 

 dilian Reptiles consist of a body of compact dentine, forming a 

 crown covered by a coat of enamel, and a root invested by a 

 moderately thick layer of cement. The root slightly enlarges, or 

 maintains the same breadth, to its base, which is deeply exca- 

 vated by a conical pulp-cavity extending into the crown, (as indi- 



(1) These teeth are likewise from the secondary rock, called Forest-marble, near Brad- 

 ford, Wilts, and I am indebted to Mr. Channin^ Pearce of that town, for the opportunity 

 of examining them. The teeth from the Wealden, supposed to belong to the HylcEosaurus, very 

 closely resemble those of Cardiodnn in the sujierficial markings, and approach them in the 

 shape of the crown. 



u 2 



