368 



THE PORTLAND OOLITE PERIOD. 



CHAP. 



PLESIOSAURUS. 



Under this title those marine reptiles are here included which 

 had a small head, long neck composed of many vertebrae, and 

 extended paddles with five rows of toes. The cervical vertebrae 

 are small near the head ; more or less concave on the articulating 

 surfaces. The dorsal vertebrae are slightly concave or almost plane 

 on the articulating faces. The anterior zygapophyses unite into 

 a spoon-shaped projection. 



In one section (a) the cervical pleurapophyses are seated on a 

 divided cicatrix ; in another (d) they have a single horizontally- 

 elongated marginal surface of attachment, to which they are usually 

 anchylosed. To this section all the species in the strata near Oxford 

 belong ; the lias contains examples of the other section. 



PLESIOSAURUS BRACHYSPONDYLUS. Owen. 



The Oxford collection contains a considerable number of cervical, 

 dorsal, and caudal vertebrae of a species approaching to or equalling 

 in size the pleiosaurs of Shotover. 



Diagram CLXVIII. Cervical vertebra of Plesiosaurus brachyspondylus. 



Scale one-fifth of nature. 

 i. Seen behind. 2. Seen on the left side. 



Many cervical vertebrae of unequal size, constituting a broken series, 

 mostly anterior, but not beginning very near the head, have been 

 obtained from Shotover. The smallest has a breadth of 1*95 inches, 



