Cope.] "* [August 15, 



Measurements. M. 



f anteroposterior .0335 



Diameters of a posterior , ^^^ ^ ^ m 



dorsal centrum j fat end 026 



I transverse^ 



I at middle 015 



Measurements of piece f ] engtli 132 



^Po„- „ ~p ~ -I diameter f anteroposterior 023 



oi spme ot same.... ! -< r 



[at base. *- transverse 019 



f vertical.. j at end 032 



Diameters of median I *- behind arch 025 



anteroposterior 0465 



at end, at flare 037 



at middle 016 



dorsal . 



1 



transverse^ ' 



Diameters of summit of spine < ^ 



L transverse 032 



The ramous character of the neural spines of this species is much like 

 what is seen in the Dimetrodon cruciger Cope. The rami in this species, 

 however, retain their size upwards, and become compressed, a feature not 

 seen in the I). cruciger. The apices of the spines in the latter species are 

 not dilated as in the E. microdus. 



Found by "W. F. Cummins in the Permian beds of Texas. 



The posterior foot in Pelycosatjria. — The foot-bones of the rep- 

 tiles of the suborder Pelycosauria are abundant in the collections from 

 the Permian formation, and I have examined my collection for specimens 

 in which they are in normal connection, for the purpose of identifying 

 them. I have been so fortunate as to find an entire tarsus, with the 

 proximal parts of the metatarsi, in the skeleton which served as the 

 type of my description of Olepsydrops natalis* The characters presented 

 by this foot are no doubt present in all of the Clepsydropidae, which in- 

 cludes the genera Theropleura, Dimetrodon, Embolophorus, and proba- 

 bly others. Tarsal bones identical with those of the G. natalis were found 

 with the original specimens of G collettii and others of much larger size, 

 accompany remains of species of Dimetrodon, or Embolophorus. 



The astragalus and calcaneum are large and well specialized bones, dis- 

 tinct from each other and from the other tarsal elements. They do not 

 resemble the corresponding bones of any known type of vertebrate, as 

 will presently appear. The navicular bone is distinct, and the cuboid 

 apparently consists of a single element. This depends on the interpreta- 

 tion given to a small bone on its posterior face, which is broken on its free 

 edge, and may be the head of the fifth metatarsus. There are three ele- 

 ments in contact with the distal face of the navicular, which correspon d 

 with the three mammalian cuneiforms. The space available for this con- 

 tact seems hardly sufficient for the three elements present, one of which 

 is out of position and" on the inferior side of the carpus. This element 



* Proceedings American Philosopk. Society, 1879, 509. 



