ON A NEW SPECIES OF PLESIOSAURUS 537 



Plesiosaiirns, and presents a median ridge with a deep fossa on either 

 side. There are a similar ridge and fossae in Plesiosaurus, the latter 

 having, I imagine, been mistaken for the posterior nares. 



9. I believe the posterior nares were situated far forwards in the 

 Plesiosaurus ; for in the first place, the object of their being situated 

 as in the Crocodile is not intelligible teleologically : and on morpho- 

 logical grounds we should expect to find them anteriorly situated, 

 for the Gavial has them more forward than the Crocodile, and the 

 Teleosmiriis than the Gavial. In the latter, indeed, they are so far 

 forward, that the pterygoids do not enclose them below at all. They 

 are nearly on a line with the middle of the orbits. 



10. The pterygoids of the Plesiosaurus send processes backwards 

 to abut against the quadratum.^ The ends of the corresponding 

 bones are broken off in the Teleosauria I have examined. 



11. The descending process of the basi-occipital is single in the 

 ■ordinary Crocodile, but in the Teleosaurus it is divided into two 

 widely separated tubercles as in Plesiosaurtts. 



12. The supra-occipital is widely separated from the edge of the 

 occipital foramen by the exoccipitals in the Crocodile. In the Teleo- 

 saurus it comes close to that edge. In the Plesiosaurus it forms part 

 of it. 



13. The petrosal bone is covered externally by the quadratum in 

 the Crocodile. In the Teleosaju'ics it is almost completely exposed 

 as in the Plesiosaurus. 



These facts seem to me to have an especial interest when we con- 

 sider the palaeontological relations of the Teleosauria to the long- 

 necked Enaliosauria, on the one hand, and to the Crocodilia on the 

 other. Anatomically, as chronologically, the Teleosaurian bridges over 

 the gap between Nothosaurus and Alligator. 



' These processes are particularly well shown in the very instructive specimen labelled 

 14,550 in the British Museum. I propose to figure this as well as some others in my 

 JMemoir. 



