1887.] ' NATURAL SCIENCES OF PHILADELPHIA. 289 



The (4) Peralestidae embrace Peralestes and Peraspalax wliich 

 are closely related if not synonymous. The lower premolars have dis- 

 tinct basal cups. The inner and outer molar cusps, instead of 

 being united by a ridge as in the last, are separated by a longitud- 

 inal valley. The upper molars (Peralestes) have a lofty internal 

 and several low external cusps, while the lower molars, (Peraspalax) 

 have a high external and low internal cusps. The canines are strong. 

 The lower molars are somewhat simpler but resemble those of 

 Dasyurus and Didelphys. I infer that, like these modern marsu- 

 pials, these animals were omnivorous. 



The lower molars of the higlily specialized genus Paurodon, the 

 type of the Paurodontidae (Marsh), although fewer in number, are 

 quite similar to those oi' Peraspalax and suggest an affiliation of 

 these two families. 



The Diplocynodontidae (Mai'sh) embrace Diplocynodon, Docodon, 

 and Eiineodon. The molars are transitional, illustrating the exten- 

 sion of the internal cingulum into a broad shelf leading; towards a 

 complete opposition of cusps such as we observe in Peraspalax, but 

 it is as yet uncertain whether this family is affiliated to the 

 Peralestidae. This family probably embraces Professor Owen's 

 genus Peramus, in which the molar and mandibular structure is 

 similar to that of Diplocynodon. 



Insectivorous Sub-Group. 



The two following families differ widely from those preceding. The 

 genera vary from an extremely small to middle size. The teeth 

 are adapted to an insectivorous diet, the incisors in the most typical 

 forms being procumbent and spatulate, the canines small, the pre- 

 molars lack distinct basal cusps, the last is lofty and pointed. The 

 molars have no cingulum. The condyle is high and the coronoid 

 slender. The formula is usually ^m 4 m 8. The families are sep- 

 arated by the structure of the molars.^ 



(3) Amhlotheridae. This embraces the genera Aehyrodon and 

 Amb lather i'um. The mandible is very slender and tapers to the 

 symphysis, with a high condyle. The incisors are semi-procum- 

 bent and spatulate, the canines small, the last premolars very lofty 



2. Amblotherium and Aehyrodon are represented by mandibles seen upon 

 the inner surface only. In the matrix impressions there is no evidence of outer 

 cusps, but the teeth closely resemble those of the Stylodontidae as seen upon the 

 inner surface, and these families may prove to be the same. 



