368 Wortmdn — Studies of Eocene Mammalia. 



followed this plan or some other,* but I think there can be 

 little doubt that it is a rule of very general application and a 

 fundamental character of the entire order. 



From this it follows that no names can be given to these 

 cusps unless we wish merely to indicate their position. Pro- 

 fessor Osborn, in reply to my strictures upon his cusp nomen- 

 clature, says that " although" wrong the names should still 

 stand." His terminology w^as proposed to supersede the old 

 names then in vogue, which attempted nothing more than to 

 indicate position. This proposal was elaborately made, and its 

 adoption has been strenuously insisted upon, on the ground 

 that the homologies of the cusps had been determined and 

 that Osborn's system thus expressed something more than the 

 mere fact of position. The names themselves carry with them 

 the significance of this alleged homology, wdiich, according to 

 the oft-repeated and many-times-published statements of its 

 author, constitutes one of its chief merits. In view of the 

 facts above set forth, however, I am more firmly than ever of 

 the opinion, that all such attempts are foredoomed to failure, 

 and I believe they should be abandoned as utterly useless and 

 confusing; that of Professor Osborn, being doubly erroneous, 

 is thev-sfore the most open to objection in this regard. 



The Microsyopsidse, as we have already seen, follow the 

 Primates in the plan of addition of the cusps to the pre- 

 molars and presumably to the molars also, which, to my mind, 

 effectually disproves Osborn's suggestion that they are mem- 

 bers of the Podentia. If further evidence is required, we 

 have only to refer to the great dissimilarity in the structure of 

 the molars in the two groups. In no living rodent does the 

 molar pattern approach that of Microsyojjs^ except, perhaps, 

 in the squirrels and their extinct forerunner, the Eocene 

 Pafamys, but even here the differences can be readily de- 

 tected. Among the Lemuroidea, on the other hand, the great 

 similarity in the constitution of the molar crowns to those of 

 the Microsyopsidse is apparent at a glance, Add to this, the 

 completely transitional molar pattern afforded by Sinilodectes^ 

 together with the strong evidence that the contemporary 

 Metacheiromijs was a Primate, and the proof of their relation- 

 ship is all but demonstrated. 



* Sciuravus Marsh, of the Bridger, which in many respects is closely re- 

 lated to Paramys, furnishes the beginning of a modification leading directly 

 into such types of molar crown as those seen in Steneofiber, FaUvocastor, and 

 Castor. In like manner, AFysops and Sciuravus afford the stem types from 

 which both the Histricomorphs and Myomorphs were in all probability de- 

 rived. This subject will be more fully treated in a subsequent part of the 

 present work. 



[To be continued.] 



