12 Watson, Notes on some British Mesozoic Crocodiles. 



jaw is similar to that of the PetrosucJms skull, and it 

 appears to correspond in curve. The length preserved is 

 29cms., of which 27 are tooth-bearing. Of this length 

 I /cms. are included in the symphysis. The splenial 

 comes well into the symphysis. The dental alveoli are 

 small and well separated, the bone between them being 

 roughened. A transverse section across the ramus in the 

 symphysial region is nearly a quadrant of a circle. 



The discussion just concluded leads to a curious 

 nomenclatural difficulty, which is as follows : — 



Owen described the genus and species PetrosucJms 

 laevidens on a skull and lower jaw which do not belong to 

 one another ; the skull belongs to v. Meyer's genus, 

 Phoiidosaurus, and as it is described earlier in the text, 

 should strictly be taken as the type of the species, which 

 would then be known as PJiotidosaur^is laevidens (Owen). 

 This name would be misleading, because the skull shews 

 no teeth, and even the alveoli are not exposed. 



On the whole it seems best to retain the name Petro- 

 suckus laevidens for the mandible, which does not 

 accurately correspond with any known genus and species, 

 and give a new specific name to the skull, under these 

 circumstances I propose that the skull should be known 

 in future as P Jiolidosaurtis decipiens, Watson. 



