1887.] 



NATURAL SCIENCES OF PHILADELPHIA. 



285 



large; there is usually no diastema, the premolar-molar series are 

 usually in excess of the typical number and the molars are cusped 

 rather than tubercular. If we were sure of the marsupial relation- 

 ship of the members of this group Ave might place them with the 

 sub-order Polijprotodonta, but some of the included families belong 

 near the Insectivora. 



/. Multituberculata. 



(1) Plagiaulacidce. This is probably the oldest family of this 

 group and is well characterized by the laterally compressed trenchant 

 premolars. The molars of Microlestes antiquus of Plieninger are 

 essentially similar to those of Plagiaidax. The M. Moorei molars 

 cannot be distinguished generically from those of Plagiaulax.^ 

 The least specialized Plagiaidax is Ctenacodon, Marsh.^ The modi- 

 fications in this family are well known as witnessed in the series 

 Plagiaidax, Ptilodus, JSfeoplagiaidax. 



ve> 



pnar 



Fig. 1. Right Maxilla of Bolodon. 



(2) Bolodontidce. This fiimily includes Bolodon and Allodon 

 Marsh.^ The premolars are not trenchant. The molars have two 

 straight rows of conical tubercles separated by a longitudinal valley. 

 Although allied to the Plagiaidacidce we cannot place these genera 

 in this family because the molar pattern is essentially different. 



6. The molars of A/. Antiqiiiis, M. Moorei aiul P. Minor in each case show a 

 closely similar disposition of the tubercles. 



1. Am. Journ. So. and Arts, Nov. 1879, p. 238. 



2. This genus is very close to Bolodon in all the details of tooth structure, 

 but shows the alveolus of a small median incisor which may be wanting in 

 Bolodon. Allodon has been placed in the Plagiaulacidae by Professor Marsh, 

 Am. Journ. Sc. and Arts, April 1887, p. 329. 



