68 Vertebrate Palaeontology of Cambridgeshire 



Far more abundant than those of Icthyopterygia are the 

 remains of Sauropterygia and more especially the pliosaur 

 group in the Kimeridge Clay of the county. Of the typical 

 genus Pliosaurus, characterized, among other features, by the 

 large head, short neck, more or less triangular teeth, with one 

 surface nearly smooth and the other two fluted, as well as by 

 the great bodily size of its representatives, at least two species 

 are recorded from this formation in Cambridgeshire. Firstly, 

 there is the typical Pliosaurus brachydirus, which is con- 

 siderably smaller than the undermentioned P. macromerus, 

 and has been recorded from both Ely and Cottenham. The 

 typical locality appears to be Oxfordshire. On the other 

 hand, the gigantic P. macromerus is typified by a femur from 

 Swindon. In both species the teeth are of the same general 

 type, but whereas there are 35 of these in the lower jaw of 

 P. brachydirus, in that of P. macromerus there appear to be 

 only 24. "Teeth and vertebrae, and less commonly paddle- 

 bones, of the larger species are not unfrequent in the pits 

 near Ely. The name P. brachyspondylus has been applied to 

 immature vertebrae of this genus from Ely in the Sedg- 

 wick Museum. Nearly allied to Pliosaurus is the genus 

 Peloneustes, as typified by P. philarchus of the Oxford Clay. 

 Among other features, this genus is distinguished by the 

 much greater length of the bony union, or symphysis, of the 

 lower jaw, which includes the sockets of about a dozen teeth. 

 The teeth differ from those of the more typical species of 

 Pliosaurus by their nearly conical form and uniform fluting. 

 In the Kimeridge Clay the genus is represented by P. aequali*, 

 typified by a femur from Oxfordshire, but also occurring at 

 Ely ; the remains from the latter locality having received the 

 name of Plesiosaurus sterrodirus 1 . 



Plesiosaurs seem to be much less common in the Kimeridge 

 Clay of Cambridgeshire than they are in the Oxfordian of 

 Huntingdonshire. The large Colymbosaurus trochanh'riu* (at 

 one time included in the Cretaceous genus Cimoliosaurux) is, 

 however, represented at Ely. Plesiosaurs of this and the 

 1 See Gat. Foss. Eept. Brit. Mus. n. 153. 



