12 Watson, The Saitropteiygia of the Whitby Museuvi. 



The skull also resembles those of these two species 

 pretty closely. 



Marked differences are, however, to be found in the 

 cervical vertebrae. 



Those of P, megacephalus differ from ours in the 

 following characters : — 



The centra are less shortened longitudinally, the 

 arches are much larger in proportion to the centra ; the 

 long axes of the zygapophyses are directed laterally, 

 whereas in P. propinqu/is they po\nt forward and backward. 



These rather marked differences may indicate generic 

 distinction of the two species. 



The cervicals of Rhouialeosauriis Craviptoni differ in 

 having much smaller zygapophyses, and in the position 

 of the neural spine directly over the centre of the centrum. 



On the whole the cervical neural arches of P. propin- 

 quiis resemble shortened vertebrae of Sthenarosaurus 

 Dawktnsi more than those of any other plesiosaur with 

 which I am acquainted. 



The whole problem of the large-headed Sauropterygia 

 is a difficult one, and I do not propose to discuss it until 

 I have examined the other species, both from the Lias 

 and the Lower Oolites ; meanwhile the species is probably 

 best referred to as " Plesiosauriis " propinqiins, Blake. 



The other Sauropterygian remains in the Whitby 

 Museum are as follow : — 



No. 854. A set of vertebrae bearing the following 



label :— 



14 Caudal Vertebrae 



of 



Plesiosaurus homalospondylus. Owen. 



Upper Lias, 



Saltwick. 



