218 PROF. H. G. SEELET ON PATRTCOSATTRTJS MEROCRATUS 



middle of the superior aspect. Secondly, the great trochanter ex- 

 tends further proximally, but is not developed to quite the same depth 

 distaUy. The well-marked longitudinal posterior concavit}' denned 

 by the reflected posterior margin of the trochanter is also a distinctive 

 feature. The comparatively thin proximal epiphysis seems to mark 

 the beginning of a condition of the extremities which has attained 

 greater development in modern lizards. Yet the configuration of 

 the bone is in no sense embryonic or indicative of imperfect ossifi- 

 cation, but rather shows that the modern lizards have diverged from 

 this ancient type so far that it is likely to belong rather to a sub- 

 ordinal modification than to an extinct family. 



First Sacral Vertebra (PI. XII. figs. 11, 12). 



It is impossible to say that the vertebra which is now to be 

 described pertained to the same species as the femur, for there is 

 no record of the exact locality in the neighbourhood of Cambridge 

 from which the specimens were obtained ; but since there is nothing 

 inconsistent with natural association in the characteristics of the 

 two bones, and the sacrum, while conforming to the general plan of 

 existing lizards, yet differs from them in notable characteristics of 

 the neural arch, I have not hesitated to describe them as probably 

 the remains of the same species. 



The fossil consists of the first sacral vertebra made up of the 

 complete centrum, the neural arch, which has lost the neural spine, 

 and the prezygapophyses ; and the transverse processes which are 

 fractured through the middle were probably complete when the 

 specimen was discovered. These parts are united together by con- 

 spicuous sutures (fig. 11). 



The centrum is depressed, 11 millim. long and 14 millim. wide, to 

 the sutures with the sacral ribs, which form quadrate transverse 

 processes. The inferior surface is concave in length and convex 

 from side to side in the middle, becoming depressed laterally and 

 constricted posteriorly from side to side, so that behind the trans- 

 verse processes the bone narrows towards the posterior surface to a 

 width of 9 millim. 



The anterior articular cup is about 11 millim. wide and 7 millim. 

 deep, transversely reniform, with a concavity above impressed by the 

 neural canal, and the convexity below. It may have been slightly 

 deeper, since the inferior margin is worn. It is moderately concave 

 from side to side and from above downward, and shows in the middle 

 a small notochordal pit. The posterior articular surface is much 

 smaller and, though not perfectly preserved, may be described as 

 semicircular, 9 millim. wide and nearly 5 millim. deep, very slightly 

 convex from side to side, but on the whole flattened, with a small 

 central notochordal pit. 



The neural arch is sharply defined by the sutures which separate 

 it from the transverse processes : but the suture which divides it 

 from the centrum placed at the summit of the anterior articular 

 cup is only seen on the right side. The width of the neural arch 



