1887.] NATURAL SCIENCES OF PHILADELPHIA. 291 



TRIASSIC MAMMALS. 



Droviatherkivi is widely aberrant, and is the most reptilian in ap- 

 pearance of all the Mesozoic genera. Professor Marsh has proposed 

 the family Dromatheridae to embrace this genus, but without defining 

 it. Uniting it with Microconodon, the family may be characterized 

 by the imperfect division of the fangs of the molars and the wide 

 diastema behind the canine. The reptilian (Theromorph) condi- 

 tion of the molar fangs may be found to separate these genera still 

 more widely from the Jurassic forms so as to represent a new order of 

 mammals, the Protodonta. 



Conclusion. 



It is now generally admitted that many of the genera embraced 

 in the MultituberGulata were Marsupials, and on many grounds it 

 is safe to place this group as a Sub-Order of the Marsupialia. 

 Are the Jurassic members of the second group also to be placed in this 

 order or do they form a distinct order by themselves? Professor 

 Marsh in his recent view of the Mesozoic mammals has held the 

 latter view. It is, however, impossible to find a single common char- 

 acter^ or set of chai-acters for these genera which is of ordinal value. 

 On the other hand, there are many grounds for placing the Tri- 

 conodontidae, Peralestidae and Athrodontidae, and their affiliated 

 families, in or near the ancestral lines of the modern Dasyuridae 

 and Phascoloniidae respectively, while the Stylodontidae are similarly 

 related to the Chrysochloridae. These grounds may be partially 

 stated. What holds good of one genus is naturally true of all the 

 genera which are clearly allied to it. (1) Triconodon has one 

 more premolar but otherwise resembles Thylacinus both in the 

 structure of the mandible and in the form and succession of the 

 teeth. (2) Peras^mlax, although much more imperfectly known, is 

 allied to Dasyurus in its molar structure. (3) Athrodon, although 

 diflfering from Phascolomys in the possession of a lai'ge canine, shows 

 a marked resemblance to this genus in the molar structure. We 

 may designate the allied carnivorous, omnivorous and herbivorous 

 sub-groups as proto-Marsupialia, a sub-order distinguished by the 

 almost invariable presence of four premolars, a number unknown 

 among modern Marsupials. 



1. The mylohyoid groove is universally present, but is also found in 

 Myrmecoiitts. 



