M. R. Thorpe — Lepiaiiclienia, etc. 405 



Akt. XXyil.—Leptaiiclienia Leidy and Cydopidhis 

 (Pithecistes) Cope, with descriptions of neiv and little 

 knoivn forms in the Marsh Collection; by Malcolm 



EUTHERFOED ThOKPE. 



[Contributions from the Othniel Charles Marsh Publication Fund, Peabody 

 Museum, Yale University, New Haven, Conn.] 



Table of Contents. 



Introduction. 

 Description of species. 



Leptauchenia decora Leidy. 



L. cf. decora. 



L. major Leidy. 



L. nitida Leidy. 



Cyclopidius Cope. 

 Pithecistes Cope. 



C. lulHanus, sp. nov. 



Clielonoceplialus scliuclierti, subgen. et sp. nov. 

 Eeferenees. 



Introduction. 



The genera Leptauchenia and Cyclopidius are the most 

 peculiar of all the Oreodontidae. Pithecistes Cope is 

 considered identical with Cyclopidius. The first genus 

 is fairly well known, the whole skeleton of L. decora 

 having been mounted, but not as yet fully described. 

 Cyclopidius is known only from skulls and jaws. 



Leptauchenia decora was apparently the most numer- 

 ous, judging from the number of individuals represented 

 in the Marsh and other collections. 



The taxonomy of these genera will be discussed in a 

 later paper where the Oreodontidae as a family are con- 

 sidered. It is sufficient to remark here that they repre- 

 sent the climax of at least a part of this family, which 

 began in the Eocene, reached its greatest development 

 in the Oligocene, and became extinct through these and 

 other highly specialized and peculiar forms in the Mio- 

 cene or early Pliocene. Leptauchenia represents an 

 earlier geologic epoch than does Cyclopidius (Pithecis- 

 tes), the latter also showing more marked peculiarities. 



The material in the Yale Museum serves admirably to 

 amplify our knowledge of these genera, both in the 

 description of referred specimens and of new species. 

 The excellent illustrations were made by R. "Weber. 



