xii. ICHTHYOSAURUS. 307 



ICHTHYOSAURUS DILATATUS. Phil. 



Three cervical and ten dorsal vertebrae of this group of sanrians 

 were obtained at a considerable depth in the deep well sunk in 

 Oxford clay at St. Clement's. They are somewhat remarkable for 

 neatness of outline and a general smoothness of surface. In the 

 articulating face of the anterior cervical vertebrae the height rather 

 exceeds the breadth, and the figure is somewhat pentagonal, and 

 angular below; in the dorsal series the breadth is greater, and 

 the outline below is circular. 



Dimensions. Cervical vertebras : length, ro inch ; breadth, 2*0 ; 

 height to canal, 2*2. Dorsal vertebrae: length, 1-3; breadth, 2*9; 

 height, 2-8. 



A valuable series of vertebras of this species, beginning with the 

 anchylosed atlas and axis, and extending without interruption to 

 the 25th, has been obtained from the upper part of the Oxford 

 clay in Cowley Field. The vertebras of St. Clement's go to the 

 4oth. 



This is perhaps not essentially different from the species, plentiful 

 in the Kimmeridge clay, to which Owen attached the name of 

 I. trigonus. That species, whose anterior cervical vertebras are 

 much higher than broad, will be more fully described hereafter. 



ICHTHYOSAURUS THYKEOSPONDYLUS a. Owen. 



One vertebra, whose place in the column was about the eighth 

 from the head, obtained from the Oxford clay at Buckingham, 

 belongs apparently to the well-marked species named above ; which 

 is more plentiful in the Kimmeridge clay of Shotover, under which 

 head it will be more fully described. Length, 1*0 inch ; breadth, 

 2*25 j height to canal, 2*3 : very deeply concave on the articulating 

 faces, with a few radiating plications. Neural canal flat and broad 

 on the base. 



PLESIOSAURUS OXONIENSIS. n. s. Phil. 



The deep clay which spreads round Oxford has yielded in its 

 frequent brick-yards several interesting remains of a plesiosaurus, 



a No locality is given for this species by Professor Owen, whose described specimen, 

 in the Bristol Museum, was probably from Weymouth, where it is not uncommon. 



X 2 



