150 BRITISH FOSSIL REPTILES. 



the Crocodiles, The general equality of size in the tooth-crowns seems a remnant 

 of the earlier mesozoic dental character ; but the number of teeth is even less than 

 in any known modern Crocodile or Alligator. Of the latter the species which I 

 have examined show eighteen teeth on each side of the upper, and as many teeth 

 on each side of the lower jaw. Of CrococUlus (Cuv.), I have not seen any species 

 with fewer than eighteen teeth on each side of the upper, and fifteen on each side of 

 the lower jaw. In no instance is so small a number recorded as sixteen teeth on 

 each side of the upper jaw, characteristic, as far as the present unique skull shows, 

 of the genus Plesiosuchus. 



Existing Crocodiles differ from Lizards in the position and relative size of the 

 opening, by which the breathing-passage from the nostril communicates with the 

 roof of the mouth. The bony palatonarial aperture is single, small, and placed far 

 back, very near the basi-occipital condyle. 



Those examples of extinct Liassic and Oolitic Crocodiles in which, from parts 

 of the fossil skull, usually fragmentary, a judgment could be formed of this 

 character, had led me to the conclusion that both in size and less retral position 

 the palatonares showed more resemblance to that in Lacertians, and thus gave 

 indications of a more generalised Saurian structure. 



CuviEB, in his description of a fossil skeleton of a Crocodile {Steneosaurus, Greof .) 

 from the Caen Oolite, recognised the palatonaris as a large aperture far in advance 

 of the position it presents in existing Crocodiles.^ 



This distinctive character was, however, called in question by later Palfeonto- 

 logists. In the ' Abhandlungen liber die Gavial-artigen Reptilien des lias- 

 formation,' fol. 1841, by Professors Beonn and Kaup ; it is argued at length (pp. 

 12, 16, 24) that the posterior median foramen is the true hinder or palatal aperture 

 of the nosti'ils ; and a letter from De Blainville is cited by those authors in 

 support of their view, in which Cuvier's determination, that it was ' an arterial 

 foramen,' is rejected, antl Professor Beonn's opinion is stated to be completely 

 confirmed by the appearances in the fossil skull of a Teleosaurns from Caen. 



After an examination of the original specimen, described by ChajDman, (' Phil. 

 Trans.,' vol. 1), and now in the Whitby Museum, I proceeded to compare the foramina 

 in question with those, the true nature of which might be determined by anatomical 

 investigation of their relations and functions in existing Crocodiles and Gavials. 



The results of these dissections and injections were communicated to the Royal 

 Society,^ and they demonstrated the accuracy of Cuvier's ascription of the 

 characters of a palatal nostril to the larger and more advanced vacuity in the bony 

 palate ; but they brought to light a more complex structure of the communications 



' " La fosse nasale posterieure est tres grande, et biea eloiguee de ne s'ouvrir que vers I'extremite 

 de la face basilaire, ou sont dans les crocodiles ordinaires les arriere-narines tres-peu avant le trou 

 des arteres . ." ' Ossetnens Fossiles,' torn, v, pt. ii, p. 133. 



2 ' Philos. Trans.,' 1850, p. 522, plates .10— 42. 



