204 AUSTRALIAN CROCODILES 



body and long powerful tail adapted for swimming, while the 

 ventricle of the heart is divided by a complete septum, and the 

 vertebrse of all the recent species are procoelous, that is hollowed 

 out in front and convex behind. 



The reptiles belonging to this subclass have been very 

 generally subdivided by recent systematists into three families — 

 the Giti-ialuUf, Crocodilithr, and AllirfntoridfB — distinguished chiefly 

 by the form of the snout, the position of the enlarged maxillary 

 tooth, and the sheathing or otherwise of certain of the anterior 

 mandibular teeth. But the differences on which these families 

 have been constituted are of too trivial a nature to justify such 

 division, and it is therefore preferable to retain all the members 

 of the subclass in the single original family Crocodiliihr. By 

 the interposition of the genus Toviistoma, the range of which is 

 restricted to Borneo, the gulf existent between the East Indian 

 Gavialid(B and the tropically cosmopolitan Crocodilidtf is com- 

 pletely bridged over. Thus the position of the former as 

 diagnostically separable from the latter family is untenable. 

 Further, the only character which separates the true crocodiles 

 from the alligators is the slightly increased number of mandibular 

 teeth in the latter group, these teeth rarely exceeding fifteen in 

 Croco(/ti«s and the West African Osteolteinus, while in the Chinese 

 and North American Allu/ator, and the tropical American Cniman 

 the minimum is seventeen, and the number rises as high as 

 twenty-twc in Odiman triqondtus ; and since in Tomiiitu)na, which, 

 without doubt, is more closely allied to the gharial, and the 

 slender-snouted crocodiles such as the Australian (rucodilus 

 joIiHstnnii, Kreft't, the African C. attaphractux, and the South 

 American C intervi dius — the increased number also prevails, 

 it follows that this character, when unsupported by others, is 

 not of sufficient value to warrant a separation of the two groups. 

 The well-known character origiually pointed out by Cuvier on 

 which so much stress has been laid, namely — that in Crocodilus 

 the enlarged fourth mandibular tooth fits into a notch in the 

 upper jaw, while in Allu/ator it is completely sheathed within a 

 pit, is not absolutely diagnostic, since specimens of the short- 

 snouted CrocodUns palustris of India, Burma, and the Tvlalay 

 Archipelago occur, which agree in this respect with the 

 alligators. On the other hand, the late Prof. Cope has described 

 a supposed alligator in which the fourth tooth on one side fits 

 into a notch, on the other into a pit, this, however, is of course 

 an accidental variation. 



