92 



MARINE REPTILES OF THE OXFORD CLAY. 



surface for the quadrate, except a small portion of the outer concavity which is on the 

 surangular. The articular surface consists of two concavities, the outer much the 

 larger and separated from the other by a slight ridge ; the surface, as a whole, looks 

 upwards and forwards. Behind this surface the articular is prolonged backwards, 

 forming the upper portion of the postarticular process and terminating behind in a 

 blunt angle. 



Vertebral Column (PI. VI. figs. 6, 6a; PL VII. figs. 5, 5 a; text-figs. 34-38). — 

 Several almost complete examples of the vertebral column in various species of 

 Steneosaurus are preserved in the Leeds Collection ; in some cases the vertebrae are 



Text-fig. 34. 



ax. a. 



ac.a.jESi 



ax. a. 



n.c. 



a.w.b. r.'f iff G x..a. 

 C. 



at.ck 



awj 



wA 



rfodrf 



Atlas and axis of Steneosaurus leedsi: A, from the left side; B, from behind. (R. 3806, \ nat. size.) 

 Also of Steneosaurus durobrivensis : C, from left side ; D, from front. (R. 3701, £ nat. size.) 

 at.a., neural arch of atlas ; a.to.b., anterior wedge-bone (hypocentrum) ; ax.a., neural arch of axis ; 

 </., diapophysis of axis ; n.c., neural canal ; od., odontoid (centrum of atlas) ; pa., posterior zyga- 

 pophysis ; r 1 ./., r\/., facets for the heads of the ribs of the atlas and axis. 



almost uncrushed and undistorted. The specimens upon which the following account 

 of the vertebral column in this genus is founded, are (1) a nearly complete ai;d 

 uncrushed series of vertebra of St. leedsi (R. 3806), consisting of the atlas, axis, 

 "and seven other cervical vertebrae (1 one wanting), fifteen dorsals, two sacrals, and 

 thirty-six caudals ; (2) the vertebral column of the type specimen of St. durobrivensis 

 (R. 3701), consisting of atlas, axis, and eight other cervicals, thirteen dorsals, two 

 sacrals, and thirty-eight caudals. 



