132 



MARINE REPTILES OF THE OXFORD CLAT. 



sacral region of the type specimen (the only one in which this part of the skeleton is 

 preserved) a remarkable condition is found, there being apparently three sacrals (text- 

 fig. 50). The explanation of this appearance seems to be, that the ribs of the first 

 caudal have greatly enlarged and resemble sacral ribs, taking part in the support 

 of the ilium. The two true sacrals are similar to those of St. durobrivensis, 

 except that the outer end of the ribs of the second, instead of having a facet 

 on its anterior face only, for union vrith the end of the rib of the first 

 sacral, has also a facet on its hinder face for union with the massive rib of the first 

 caudal ; the postero-dorsal flange of the second sacral ribs also seems to have been 

 lost, though a similar ridge may have been present on the first caudal rib. This is a 

 massive structure like the ribs of the true sacrals ; it is trihedral in section and much 

 expanded at its outer end, where it bears two irregularly roughened surfaces, one, 



Text-fig. 50. 



Sacral aud first caudal vertebra; (restored) of Steneosaurxis obtusidens, from above (R. 316S, ^ nat. size). 



c.i:, caudal rib ; U.S., iliac surface of sacral ribs ; U.S.?, doubtful iliac surface of caudal rib ; 

 s.r.l, s.r.2, first and second sacral ribs. 



the largest, apparently for union with the posterior part of the ilium, the other 

 looking forwards for union with the corresponding facet on the posterior side of the 

 outer end of the second true sacral : as above noted, the postero-superior angle may 

 have been produced into a flange such as is seen on the posterior side of the second 

 sacral rib in St. durobrivensis (PI. VI. fig. 6) and in Mycterosuchus (text-fig. 52). 

 The ilium in this specimen has a much roughened surface behind that for the second 

 sacral rib, probably for union with the outer end of the enlarged caudal rib, but in 

 another still larger specimen referred to this species there is no trace of this surface, 

 although those for the two true sacrals are well defined. From this it appears likely 

 that the condition in the type specimen may be an individual peculiarity. 



