1882.] 447 [Cope. 



The preceding paragraphs were written in May of the present year. On 

 my return home, September 1st, after an absence of three months, I find 

 that various parts of the skeleton of Periptychus* have reached my mu- 

 seum. On examination, I find that the astragalus of that genus fulfils the 

 anticipation above expressed. It is without trochlea, and nearly resembles 

 that of Elephas. As it agrees nearly with that of Phenacodus in other re- 

 spects I only separate it as a family from the Phenacodontidce. One other- 

 type remains to be discovered which shall connect the Periptychidce and 

 the hypothetical Hyodonta, and that is a Taxeopod without a head to the 

 astragalus, — unless, indeed, the "Hyodonta" should prove to have such a 

 head. I think the latter the less probable hypothesis, and hence retain 

 the term Platyarthra for the hypothetical Taxeopod without trochlea or 

 head of the astragalus. 



These relations may be rendered clearer by the following diagram : 



Taxeopoda. 

 Condylarthra. Platyarthra .f f 



Hyracoidea. \ 



Proboscidea . Amblypoda. 



/ 

 / 

 Hyodonta. ft Pantodonta. 



Dinocerata. 



DlPEARTHRA. 



Perissodactyla. Artiodactyla. 



Third contribution to the History of the Vertebrata of the Permian formation 

 of Texas. By E. D. Cope. 



{Read before the American Philosophical Society, September 15, 1882.) 



Since the publication of my second contribution to this subject,:): I have 

 described four additional species. These are, in Bulletin of the IT. S. 

 Geological Survey of the Territories ;§ Pantylus cordatus and Dimetrodon 

 semiradicatus ; in the American Naturalist, || Eryops reticulatus and Za- 



* See American Naturalist, October, 1882 

 ft Hypothetical. 



JPaleontological Bulletin, No. 32, Proceedings American Philosophical So- 

 ciety, 1880; the plates, 1881. 

 I Vol. vi, 1881, p. 79. 

 » 1881, p. 1020. 



