FOSSIL REPTILES OF DORSET. 21 



following species from the Kimmeridge Clays in the neighbourhood 

 of "Weymouth : 



ICHTHYOSAURUS TRIGONUS, Owen. 



This is not an uncommon species in the Kimmeridge Clays of 

 Shotover and Swindon, varying from twenty feet to five feet in 

 length. The dorsal and tail vertebrae are oval, the height and 

 width being double its length ; those of the neck are pentagonal 

 and flattened towards the edges. 



ICHTHYOSAURUS THYREOSPONDYLUS, Owen. 



This species is remarkable for the shortness of the vertebrae, the 

 length averaging less than two -fifths of the diameter ; in other 

 respects the vertebrae resemble those of Ich. trigonus. 



ORDER SAUROPTERYGIA, Owen. 



This Order, like the preceding, had no bony or horny covering. 

 The vertebrae are either flat or very slightly concave at both ends ; 

 the neural arch through which the spinal cord passed was 

 anchylosed to the centrum. There was neither a sternum nor 

 sternal ribs, the sternum being supplied by a pair of coracoids 

 which meet and join by a longitudinally extended margin. 

 The clavicles and scapula were perhaps represented by a 

 triradiate bone, which, uniting with the coracoid, combined to 

 form the shoulder-joint. The neck was usually very long, and 

 composed of numerous vertebrae ; the sacrum of two vertebrae ; 

 the orbits large, usually with no scleroid plates ; limbs in form of 

 swimming paddles with elongated phalangal bones constricted in 

 the middle ; the hind-limb very nearly resembled the fore-limb ; 

 teeth inserted in distinct sockets in one line. 



GENUS PLESIOSAUB.US, Conybeare. 



Plesiosaurus comprises gigantic marine reptiles chiefly character- 

 istic of the Lias and Oolite. The snout is prolonged and the jaws 

 furnished with numerous teeth ; the number of the vertebrae of the 

 neck varies with the species from twenty-four to upwards of 

 forty ; each is furnished with a rib resembling those found in the 



