NATURAL SCIENCES OF PHILADELPHIA. 441 



and five of small size. The genus 31esonyxJ which I discovered 

 in the Bridger beds of Wyoming, cannot be referred to the Greo- 

 donta as here constituted, since the trochlear face of the astragalus 

 is completely grooved above as in the true Carnioora, and its 

 distal end presents two distinct facets, one for the cuboid and the 

 other for the navicular bones. It represents on this account a 

 peculiar family, the Mesonychidse. 



To the Greodonta must be referred the genera Pterodon and 

 Palseonictis of De Blainville, from the French Eocene. This 

 author and Pomel placed them in the Marsupialia, but Professor 

 Gervais remarks (Geologic et Paleontologie Francaise) that the 

 evidence is insufficient for such a course. Here also doubtless 

 belong supposed Carnivora from the Wyoming Eocene, stated by 

 Marsh to be allied to the Viverridse. ' 



The remarkable type first introduced to the notice of paleonto- 

 logists by Leid} r , represented by the genera Anchippodus, Ecto- 

 ganus, etc., has been looked upon as an order of Mammalia by 

 Marsh, and termed the Tillodontia. He gives, 2 as its characters, 

 the possession of claws, plantigrade feet with five toes, a third 

 trochanter of the femur, and separate scaphoid and lunar bones. 

 Also, that the dentition is characterized by " molars of the ungu- 

 late type," small canines, and large scalpriform incisors in both 

 jaws, faced with enamel and growing from persistent pulps as in 

 the Rodentia. He says this order " seems to combine characters 

 of the orders of carnivores, ungulates, and rodents." 



Except in the dentition, the definition above given applies to 

 the Greodonta ; and an analysis of the dentition shows so many 

 points of resemblance as to render it probable that they pertain 

 to the same order of Mammalia. Also, except in the dentition, 

 the characters given by Prof. Marsh do not differ from those of 

 the Insectivora. The structure of the superior molars is not in- 

 consistent with the same order, and the small canines and large 

 incisors are even more like those of most Insectivora than are 

 Greodonta. The singular form of these incisors, and their growth 

 from persistent pulps, is rather characteristic of Rodentia. The 

 transverse or tubercular premolars also distinguish this group 

 from both the Greodonta and the true Insectivora. The defini- 

 tions of the order and sub-orders will then be as follows: 



Insectivora. Mammalia with small cerebral hemispheres which 

 do not cover the olfactory lobes, nor the cerebellum ; with numer- 

 ous clawed digits, and a third trochanter of the femur; with a 

 transverse glenoid cavity for the mandible. 



Superior incisors normal, not growing from persistent pulps; 

 canines large; premolars compressed. Astragalus not grooved 

 above, articulating with the cuboid as well as the navicular ; five 

 toes on the hind foot; Greodonta. 



1 Ann. Ropt U. S. Geol. Surv. Terrs., 1872, p. 550. 



2 Amer. Journ. Sci. Arts, 1875, 231. 



