398 W'illixlon — Reptiles from the Permian. 



comparison of the similar feet of Diadectes with those of the 

 gopher. The right front foot, as preserved in the matrix, had 

 the tibia and fibula, with their attached proximal carpals, pressed 

 downward somewhat below the proximal ends of the metatarsals, 

 but not a vestige is preserved in the matrix of centrale or 

 tarsalia, nor is there any tarsal bone preserved with either speci- 

 men save the four sets of proximal ones. It is not at all impos- 

 sible, however, that vestigial, nodular tarsalia may have been 

 ossified, but it is not very probable that they were. Chondrifica- 

 tion was evidently here a specialization, and in accordance with 

 the almost universal rule among terrestrial vertebrates we 

 should expect that the process would develop more rapidly in 

 the hind than in the front feet. 



No indications whatever of ventral ribs are present in 

 either specimen. In their place, however, the whole ventral 

 region was covered by a sort of plastral sheath of imperfectly 

 ossified or calcified material. Patches of this sheath were 

 found scattered about in the matrix below the posterior verte- 

 brae 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 scutes. 



Habits and Relationships of Limnoscelis.- — It is almost 

 superfluous for me to point out, so evident will it be to 

 every one, that Limnoscelis must have been a subaquatic or 

 marsh-dwelling reptile. Of the poorly ossified or cartila- 

 ginous 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 with Diadectes especially in the general 

 structure of the limbs, the arrangement of the skull bones, 

 especially the union of the prefrontal and postfrontal over the 

 orbit, the general structure of the vertebrae, with the cylindric 

 or prismatic spines, etc. It agrees with both Diadectes and 

 Pareiasaurus in the very characteristic flattened occipital con- 

 dyle ; and T believe that when we know more of the structure 

 of the skull of the latter genus, we shall also find more evi- 

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

 three genera, and Propappus also, may perhaps be placed in 

 the same suborder of reptiles. 



