334 THE PORTLAND OOLITE PERIOD. CHAP. 



ICHTEYOSAURUS. 



Remains of this genus of marine saurians are common in the 

 Kimmeridge clay of Shotover and Cumnor ; but only few cases 

 occur even of several vertebrae in their true relative positions. 

 Portions of the head may be said to be almost unknown; ribs, 

 scapulae, coracoids, and separate limb and paddle bones are occa- 

 sionally found, but not so connected with the vertebrae as to render 

 it worth while to describe them minutely. Diagrams of the more 

 important will be added after the notices of vertebrae. 



On Icktkyosaurian Vertebra in the Oxford clay and Kimmeridge 

 clay generally. 



Placing before the eye about 250 vertebrae of ichthyosaurus 

 collected from the clay pits round Oxford, there may be counted 

 about 75 cervical, 75 anterior and middle dorsal, 100 post dorsal 

 and caudal. 



In this collection short chains of vertebrae may here and there 

 be found, but only one of sufficient extent from one animal to make 

 it a standard for the reunion of scattered elements. The series 

 referred to was obtained from Cowley field, south-east of St. 

 Clement's, where the upper part of the Oxford clay, dug for making 

 bricks, yields abundance of Ammonites vertebralis. 



It consists of the basi-occipital bone, followed by anchylosed 

 first and second vertebrae, then by twenty other cervical and three 

 anterior dorsals. 



After an interval estimated at five vertebrae another series 

 of ten dorsals, belonging to the same species, from the same clay 

 at a greater depth, opened in a well at St. Clement's, comes in. 

 Three cervicals belonging to the same individual satisfactorily con- 

 firm the identity of species, which resembles Ichthyosaurus trigonus 

 of Owen. Thus we reach the 4Oth vertebra, and the full magnitude 

 of the column of this individual. 



After this, by frequent inspection of many detached vertebrae, 

 we pass gradually to about the 6oth, where a different general form 

 sets in ; soon after the lateral cicatrices unite, toward the basal 

 -edge ; and finally this mark is lost toward the extremity of the 



