A DESCRIPTIVE CATALOGUE 



OF TUE 



ARINE REPTILES 



OF 



THE OXFORD CLAY. 



Order IC H T H Y O PT E R YG I A. 



Caenivokous marine reptiles with a cetacean-like body and no visible neck ; a dorsal 

 fin without skeletal supports, and a large vertical caudal fin, of which the lower lobe 

 is strengthened by the downwardly-turned end of the vertebral column. A plastron of 

 ventral ribs present, but no dermal armour. 



Skull large, with a more or less elongated rostrum composed mainly of the pre- 

 maxillfe. External nares a little in front of the very large orbits, in which there is 

 always a ring of ossified sclerotic plates. A large parietal foramen. Supratemporal 

 fossa large, post-temporal fossa small, and lateral temporal fossa absent ; a vacuity 

 enclosed between the quadrate and quadrato-jugal. Postorbital and postfrontal bones 

 distinct; lachrymal and prefrontal also distinct. Quadrate immovable, being closely 

 united below with the pterygoid, above with the squamosal and supratemporal, which 

 remain separate. In the otic region, pro-otic and opisthotic elements distinct ; stapes 

 (where known) short and stout, extending from basioccipital to quadrate. In the palate, 

 pterygoids extending forwards to meet the vomers and excluding the palatines from 

 the middle line ; an epipterygoid [columella cranii) present ; a large parasphenoid 

 extending forwards between the pterygoids ; apparently no trausverse bone. Teeth 

 simply conical, usually with a vertical Labyrinthodont-like folding of their walls ; 

 restricted to the edge of the jaws ; heterodont and set in distinct sockets in some 

 early genera (e. g. Mixosaurus) ; homodont and set in continuous dental grooves in the 

 typical and later genera. 



B 



