1885.] -*--*- [Cope. 



to the Coal Measures or to the Permian. There is nothing in the charac- 

 ters of the genus Stereosternum to contradict such a supposition. The 

 primitive characters of various parts of the skeleton and the obvious re- 

 semblances to Ichthycanthus, add probability to such a view. 



Specific characters. — These may be first drawn from the specimen of the 

 slab already alluded to. 



The relative length of the body is not certainly known, as it is only par- 

 tially preserved in the specimens sent by Prof. Derby. To judge from 

 the one above referred to, it has the ordinary proportions of a lacertilian. 

 The hind legs are well developed, as for example in an Iguana. The tail 

 is well developed, but its length is not determinable as the distal por- 

 tions are lost. 



In the slab specimen the dorsal vertebrae are split or otherwise damaged, 

 so that I describe them preferably from other specimens. The few that are 

 well preserved show characters identical with the latter. I derive the fol- 

 lowing however from the slab specimen. The dorsal vertebra? have the 

 neural spines well developed but not much elevated. In profile their ver- 

 tical diameter is about equal to their anteroposterior, and the superior bor- 

 der is squarely truncate. They diminish in height posteriorly. The 

 spines are present at the lumbar vertebra?. The shafts of the ribs have 

 a round section. The proximal portions are for a short distance abruptly 

 incurved to the vertebral body. The distal extremity is pointed. The tissue 

 is dense, and there is no medullary cavity. In the lumbar vertebra? the rib is 

 much more slender, and is shorter. It is coossified with the centrum. The 

 caudal vertebrae have strong diapophyses, which are acuminate and de- 

 pressed. In the anterior caudals they are recurved at the extremity, but 

 shorten rapidly posteriorly and are transverse. In the specimen they are all 

 separated from the centrum by a fissure which appears to be too constant 

 and too regular to be regarded as a fracture. I suspect therefore that the 

 diapophyses are free, and are joined to the centrum by a simple truncate 

 head, which has an outline nearly round. This view is confirmed by the 

 presence on each side of the centrum of the median caudal vertebra?, of a 

 bone which resembles the sesamoids of the feet of Mammalia, which is quite 

 free from the centrum, and is applied longitudinally to its anterior half. 

 It is probably the rudimental diapophysis. The posterior caudals have no 

 diapophyses. The latter are the only ones in the specimen which are well 

 preserved. 



The bodies of the caudal vertebra? have a low ridge in the place ot the 

 fissure which is seen in some other specimens to divide them into equal an- 

 terior and posterior halves. The entire centrum is longer than deep or 

 wide, and is a little deeper than wide in section. The neural arch is 

 divided into two parts by the characters of the surface. The anterior 

 half is swollen and roughened by minute pits, and is separated from the 

 less prominent posterior half by a pair of small fossa?, one above the other. 

 The neural spine stands entirely on the posterior half, and is thus widely 

 removed from the prezygapophysis, which is above the anterior border of 



