Marsh Collection^ Pecibody Museum. 365 



exception of the character of the astragakis, which, as we have 

 just seen, is open to question, all the characters cited, save 

 one — the molariforiii fonrth premolar — are evidence of rela- 

 tionship with, and apply equally to Cheiromys as well as to the 

 Rodentia. The molariforni fourth premolar is not an espe- 

 cially rodent character. It occurs among the Lemuroidea in 

 Hajpaleimir griseus, Otogale Monteiri^ Galago Alleni^ and 

 Hemigalago Demidoffi. In like manner, the evidence against 

 rodent relationship, as given by Osborn, can be quite as well 

 considered to be evidence against relationship to Cheiromys^ 

 for Owen has long since conclusively demonstrated that this 

 species is a Primate, with a highly modified rodent-like denti- 

 tion. Altogether, I fail to see wherein Osborn has given any 

 reasons, beyond those already well known, for regarding the 

 Microsyopsidse as members of the Rodentia. On the contrary, 

 to my mind, there is fairly conclusive proof that these animals 

 are not rodents. I shall now proceed to a statement of this 

 evidence. 



In Part I of the present series of papers (p. 96, Separata), I 

 have presented my views at some length upoii the theory of 

 "Cusp Migration," as originally propounded by Osborn."^ I 

 have likewise dissented from the use of the terminology of the 

 mammalian molar cusps proposed by him, on the ground that 

 their homologies were incorrectly determined and the names 

 applied inappropriate and misleading. I have further expressed 

 the opinion that, as far as any nomenclature is applicable to 

 these cusps, which would convey any information of their 

 homological relationship, that proposed by Scott is preferable 

 because based upon ascertained and undisputed facts in the 

 history of the premolar series. By far the most important 

 principle embodied in Scott's determination of the order of 

 appearance and homological position of the cusps of the pre- 

 molars, although never expressed nor stated by him, is that by 

 means of which we are provided with the key to a proper 

 interpretation of the molar cusps and the determination of 

 their history. All theoretical considerations, as well as all the 

 evidence obtainable, point with such directness and definite 

 precision to the conclusion that the molars and molariform 

 premolars have passed through identically the same changes 

 and have been subjected to precisely the same infiuences, that 

 it may be accepted as one of the basic and fundamental truths 

 of dental morphology. Credence in any other view would be 

 equivalent to believing that the corresponding teeth on the 

 opposite sides of the mouth have had different histories. This 

 principle or law has not as yet been ocularly demonstrated, for 

 the reason that no Eutherian mammals older than those from 



* Jour. Acad. Nat. Sci. Phila., 1886, p. 242. 



