REPTILIA : LIMNOSCELIS 47 



covered by a sort of plastral sheath of imperfectly ossified or calci- 

 fied material. Patches of this sheath were found scattered about 

 in the matrix below the posterior vertebrae and adjacent regions, 

 some of them two inches or more in diameter. I have not yet had 

 an opportunity to examine the substance microscopically but to 

 the unaided eye it appears to be loose bone tissue. It is quite 

 certain that the animal did not have distinct ventral ribs, or osseous 

 dorsal scales. 



Habits and relationships of Limnoscelis. — It is almost superfluous 

 for me to point out, so evident will it be to everyone, that Limno- 

 scelis must have been a subaquatic or marsh-dwelling reptile. 

 Of the poorly ossified or cartilaginous carpus and tarsus the evidence 

 is almost positive, and there can be but one explanation, subaquatic 

 habits. The limbs as a whole indeed are strongly suggestive of the 

 turtles. The relationships of the genus are unquestionably closest 

 with Diadectes of any forms that we know, from which it differs 

 chiefly in the elongated skull, the conical, prehensile teeth, the 

 absence of the ear cavity posteriorly, the small size of the parietal 

 foramen, the smoothness of the skull surface, the non-expanded 

 ribs, their apparently single-headedness throughout, the absence 

 of hyposphenes, and the feebly ossified carpus and tarsus. It 

 agrees well with Diadectes in the general structure of the limbs, 

 the arrangement of the skull bones, especially the union of the pre- 

 frontal and postfrontal over the orbit, the general structure of the 

 vertebrae, with cylindric or prismatic spines, etc. It agrees with 

 both Diadectes and Pareiasaurus in the very characteristic flattened 

 occipital condyle; and I believe that when we know more of the 

 structure of the skull of the latter genus we shall also find more 

 evidences of affinity in these groups, to such an extent that the 

 three genera and Pro pap pus also may perhaps be placed in the 

 same suborder of reptiles; possibly also Panlylus. 



