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PROF. H. G. SEELEY ON PATRICOSAURUS MEROCRATUS 



19. On Patricosaurus merocratus, Seeley, a Lizard from the Cam- 

 bridge Greensand, preserved in the "Woodwardian Museum 

 of the University of Cambridge. By H. G. Seeley, F.R.S., 

 F.G.S., Professor of Geography in King's College, London. 

 (Read March 9, 1887.) 



[Plate XII.] 



jSo lacertilian has hitherto been recorded from the Cambridge 

 Greensand. The comparative rarity of this group of animals in the 

 deposit is evidenced by the fact that only two fragments of lizard- 

 bones are known to me to have been found during the whole period 

 in which its fossils have been collected. One of these is a sacral 

 vertebra with the transverse processes broken away, which was, I 

 believe, collected by the Rev. H. G. Day prior to 1859. The other 

 is the proximal end of a femur obtained recently by Mr. A. F. 

 Griffith. Slight as is the material, it is worth recording as evidence 

 of a terrestrial animal of a relatively large size, and more nearly 

 allied to existing lizards than are the other Cretaceous representa- 

 tives of this order of animals. 



Eight Femur (PI. XII. figs. 9, 10). 



The proximal end of the right femur now described is larger than 

 the corresponding bone in the largest existing Monitor. It was 

 unfortunately fractured, subsequently to being mineralized, at a 

 point below the articular head, just where the shaft becomes trian- 

 gular, so that the length of the bone and its distal characters are 

 entirely conjectural. The shaft consists of dense bony tissue, as in 

 existing lizards, with a small medullary cavity. The fragment is 

 about 3 centim. long. It has the characteristic vertical compression 

 and forward curvature of the convex articular head, and the usual 

 front-to-back compression of the inferior trochanter, which, however, 

 extends further proximally than in existing lizards. The fragment 

 has experienced a little attrition, and a thin external epiphysial 

 layer of bone is partly removed from the proximal articular surface — 

 a character of some interest as repeating the epiphysial growth 

 which is often seen in existing lizards, but in a form no thicker than 

 in the limb-bones of some breeds of domestic fowls, like Bramahs, 

 when a week or two old. 



The proximal articular surface is semicircular from front to back ; 

 it is 2 centim. wide. Its superior outline, viewed from the proximal 

 end, is comma-shaped, being a centimetre wide in front, and becoming 

 narrower as it extends backward. From above downward the 

 articulation is convex, about 12 millim. thick in the middle, and 

 narrowing away behind. The convexity of the anterior part of the 

 smooth rounded articular head is suggestive of the limb having been 

 carried in a position well raised from the ground. The axis of the 

 articular head of the bone is directed inward and very slightly 



