354 THE WASATCH AND BRIDGER FAHN^^. 



spending bones of Cants and Felis. Its cuneiform facet is somewhat concave 

 transversely. It has two facets for the third metatarsal, as in Hycena; that 

 is, they are a good deal more distinct than in Felis, where they are more 

 distinct than in Canis. The distal condyles are furnished with a posterior 

 and inferior carina, which is wanting above; the articular face is wide above 

 as in Canis, and is bounded by a transverse fossa as in digitigrade genera. 

 The phalanges of the first series are elongate and curved as in Felis, being 

 relatively longer than in Ursus. Phalanges of the other series are qnite short. 

 The ungues are short and flattened, their inferior surface is nearly plane, 

 and the superior but little convex. A shallow groove divides the upper face 

 longitudinally to the extremity. The margin below is acute to a slightly 

 contracted neck. There is no indication of collar for reception of the horny 

 sheath, except perhaps a slight area of fracture on each side, and there is 

 no projecting tuberosity below for insertion of flexor tendon. The middle 

 of the proximal part of the unguis is a raised plane, and on each side of it, 

 at the neck, two arterial foramina enter. There is a small foramen in the 

 groove, and several smaller ones near the margin. These ungues i-esenible 

 somewhat those of some tortoises. They were found with the other phalanges, 

 with which they agree in size and articulation, and no doubt belong to the 

 same animal. It is evident that they differ in character from those of most 

 existing Carnivora. The penultimate phalanges agree with ihem in the 

 depressed form of their proximal articular faces, wanting entirely the trian- 

 gular form so characteristic of Carnivora, especially of the cats and dogs. 

 The short flat shaft of the same is almost equally peculiar. 



It is clear that there were only four anterior digits in M. lanius, and 

 but four posterior ones in M. ohtusidens. 



Affinities. These have been already considered in their general beai'ings. 

 The genus is the type of a distinct family, which must be placed nearest to 

 the Amhhjctonidce. From this family the MesonychidcB differ in the complete 

 trochlear articulation of the ankle-joint. At first sight Mesonyx appears to 

 have some similarity to Ilycenodon in its dentition, but close examination 

 shows that the resemblance is rather to Amhlyctonus. There is no true 

 sectorial blade on any tooth of Mesonyx, the long heel furnishing the only 

 cutting edge, as in the premolars of several genera. As in Uycenodou there 



