MYCTEKOSUCHUS NASUTUS. 



137 



bases of the posterior zygapophyses. The remainder of the cervicals, though perhaps 

 slightly longer in proportion to their other dimensions than those of St. durobrivensis, 

 are otherwise similar to them. In the type specimen the dorsal vertebrae are lost or 

 very badly preserved, but in another specimen (R. 3892) they are in good preservation. 

 They are here found to be closely similar to those of St. durobrivensis, except that the 

 neural spines are considerably thickened at their summit, terminating in a smooth, 

 flat or slightly convex surface, while beneath this on their flat sides there are well- 

 marked vertical ridges : this character is especially marked in the sacral region 

 (as shown in text-figs. 51-53), and seems to be correlated with the support of a heavier 

 armour of scutes than is found in Steneosaurus. Text-fig. 51, A, shows that the inner 

 ends of the sacral ribs form a quite considerable portion of the concave anterior surface 



Text-fig. 51. 



First sacral vertebra of Mycterosuchus nasulm : A, from front : B, outer end of sacral rib. 



(E. 3892, | nat. size.) 

 a.z., anterior zygapophysis ; U.S., surface for ilium ; n.sp., neural spine ; s., suture between sacral 



rib and the vertebra ; s.r., sacral rib. 



for union with the centrum of the lumbar ; the extension outwards of the base of the 

 neural arch along the dorsal edge of the sacral rib is also seen. In the figure of the 

 second sacral (text-fig. 52) the thickening of the upper end of the neural spine is again 

 shown, as also is the peculiar form of the outer end of the sacral rib, the postero- 

 superior angle of which is produced backwards and upwards into a well-developed 

 flange {fi., text-fig. 52, B), the outer edge of which must have fitted into a corresponding 

 depression on the inner face of the ilium. The caudal vertebrae (PI. VIII. figs. 4-9) 

 differ to a considerable degree from those of Steneosaurus. In the anterior caudals the 



l'ART II. T 



