A DESCRIPTION OF THE GENUS DIMETRODON, COPE. 13 



three species, T. retroversa, T. uniformis and T. triangulata, all based on vertebrae, are 

 also placed near that genus. 



A peculiar genus, Empedocles \_Empedias] alatus Cope, with additional hyposphene 

 and hypanthrum articulations, is also described. 



In addition to the type of humerus referred to Clepsydrops, Cope describes three other 

 humeri, which represent three other genera which have been probably already named from 

 crania or vertebras. Nos. 1 and 2 are compared with that of Eurosaurus, but the epicon- 

 dyles are more largely developed. No. 3 is considered as belonging to Empedocles [Em- 

 p edicts]. 



Prof. Cojoe concludes his paper with the following remarks : " The division Pely- 

 cosauria is established primarily on the genera Clepsydrops and Dimetrodon, but their 

 cranial structures render it highly probable that Ectocynodon, Pariotichus and Bolosaurus 

 belong to it. It is also probable that the genera, Empedocles \_Empedias\ Embolopliorus 

 and others determined from vertebra? belong to it, as the latter are frequently accom- 

 panied by pelvic bones of the type of that of Dimetrodon. All the genera known from 

 teeth and crania are of carnivorous habit, excepting Bolosaurus and Diadectes ; they may 

 be referred to a single family on this account, which I call the Clepsydropsidce. Bolo- 

 saurus will form the type of another family characterized by the transverse position of the 

 crowns of the teeth, under the name of Bolosauridos. Prof. Owen has named a group of 

 Triassic and Permian reptiles the Theriodonta, characterized by the mammal-like dif- 

 ferentiation of the incisor and canine teeth. The animals thus referred by Prof. Owen 

 probably enter my suborder of Pelycosauria, although the structure of their pelvis 

 remains to be ascertained. If so, they correspond with my Clepsydropsidw, since Prof. 

 Owen does not include herbivorous forms in his division. As it is plain that the herbiv- 

 orous and carnivorous types belong to the same order, and probably suborder, it becomes 

 necessary to subordinate the term Theriodonta to that of Pelycosauria. To another 

 division of reptiles from the South African Trias, typified by the genus Pareiasaurus 

 Owen, he gives a special name, expressive of the deeply impressed surfaces of the centra 

 occupied by the remains of the chorda} dorsalis. As this, or the perforate condition, is 

 characteristic of all of the Pelycosauria, it is probable that it is present in Prof. Owen's 

 Theriodonta also. It is also evident that since the dental characters of Pareiasaurus do 

 not serve to distinguish it as an order from the genera with distinct canine teeth, this 

 group also must be looked upon as a subdivision, perhaps of family value, of the Pely- 

 cosauria or other parts of the Rhynchocephalous order." 



In regard to the geological formation of the Illinois and Texas beds, he comes to the 

 conclusion that they are Permian. 



On the 7th of November, 1878, Prof. Cope 9 read a paper before the National Acad- 



