CHAPTER I. 



THE TRANSITION FROM THE REPTILIAN TO THE MOST PRIMITIVE 

 MAMMALIAN TEETH. BEGINNINGS OF THE NOMENCLATURE. 



1. 



THE UPPER TRTASSIC MAMMALS, DROMATHERIUM AND MICROCONODON. 



[Reprinted.] 



(Read before the American Philowphical Society, April 15th, 1887. Published in the 



Proceedings, 1887, p. 109.) 



THE mammalian jaws : discovered by Professor Emmons in the Upper 

 Triassic beds of North Carolina, and ascribed to a single genus. Droma- 

 tlicrium, were recently examined by the writer and found to belong to 

 separate genera. The type mandible of Dromathcrium is preserved in the 

 Williams College Museum, and differs widely from the mandible preserved 

 in the Museum of the Philadelphia Academy. These differences have 

 already been pointed out, 2 but require to be more fully stated, as both 

 Professors Marsh and Cope have expressed doubts as to the distinct 

 separation of these genera. The accompanying lithographic figures bring 

 out the characteristic features of these mandibles much more fully than 

 in the pen drawings which accompanied my earlier description. 



In many respects these genera agree with each other, and stand 

 separate from the Jurassic mammals of both England and America. 

 There is, first, a considerable diastema behind the canine, a very rare 

 feature in the division of Mesozoic mammals to which these genera 

 belong, although always present in the division to which Plagiaulax and 

 its allies belong, viz., the sub-order Multituberculata Cope. 



J [The chief reason for considering these jaws mammalian is that they are composed of a 

 single bone, there being no evidence of the separation into dentary, articular, and angular 

 elements, as in the jaws of reptiles. H.F.O. November, 1904.] 



z Proreediiiij/j of the Academy of Natural Sciences of Philadelphia, 1886, p. 359. I find 

 upon a second examination of Prof. Emmons' original figure, that I unintentionally criticised 

 it too severely in the former article, p. 359. While far from accurate, the figure is not so 

 misleading as I at first supposed. 



