Kimeridge Clay Fauna 67 



ferruginous sand in which they are embedded, and are highly 

 impregnated with phosphate of lime. 



The next and last fossiliferous formation of any im- 

 portance in Cambridgeshire, so far at least as vertebrates 

 are concerned, is the Kimeridge Clay, of which there is a 

 fine exposure in the well-known Roswell pits, near Ely. One 

 of the most interesting reptiles from these pits is the huge 

 marine crocodile known as Dacosaurus maximus, the crowns 

 of the teeth of which measure a couple of inches in length. 

 These teeth form smooth compressed cones, carrying a strongly 

 marked vertical keel on each side. The genus and species were 

 first described on the evidence of specimens from the Upper 

 Jurassic of the continent ; it is, however, doubtful whether 

 this reptile is really entitled to be separated generically 

 from Geosaurus, which is typified by a smaller form from the 

 same horizon. Unlike ordinary crocodiles, Geosaurus had an 

 elongated body, a naked skin, and paddle-like limbs, of which 

 the front pair were much larger than the hinder ones. Certain 

 huge vertebrae and limb-bones, inclusive of a claw-phalange, 

 from Ely, in the Sedgwick Museum, indicate a dinosaur 

 allied to Pelorosaurus of the "Wealden or Cardiodon (Ceteo- 

 saurus) of the Lower Jurassic. For these specimens Professor 

 Seeley 1 proposed the name Gigantosaurus megalonyx, but 

 without giving a sufficient description or definition. Not 

 improbably the Ely reptile may be identical with one de- 

 scribed on the evidence of a thigh-bone, or femur, from the 

 Kimeridge Clay of Weymouth as Ceteosaurus humerocristatus, 

 but which may really belong to Pelorosaurus. 



Of the two great groups of extinct marine reptiles, the 

 Ichthyopterygia are represented in the Kimeridge Clay of the 

 county by Ichthyosaurus trigonus, a species found in the same 

 formation in many other parts of the country, and taking its 

 name from the peculiar shape of the bodies of the vertebrae. 

 Other remains of these reptiles from Ely have been named by 

 Professor Seeley /. chalarodirus, I. hygrodirus, etc., but have 

 never been definitely described. 



1 Seeley, "Index to Ornithosauria, etc." 73. 



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