1881.] ^^'^ [Cope. 



The claws of this species are moderately compressed, and thej-^ termi- 

 nate abruptly and obtusely. The extremity is deeply tissured, and each 

 of the two apices is rugose. 



Mesonyx ossifragtjs Cope, American Naturalist, 1881, p. 1018. 



Pachymna ossifraga Cope. Report Capt. Wheeler, U. S. G. G. Surv. W. 

 of 100th Mer. iv, ii, p. 94, 1877. 



A series of specimens of this species demonstrates the following points : 

 (1) Paclujoina was founded on a superior molar of Mesonyx, and must be 

 suppressed. (2) Mesonyx navajovius Cope must be separated as a distinct 

 genus, since the apices of the crowns of the last two molars have two 

 cusps. I have called this genus Dissacus (American Naturalist, Dec, 1881). 

 (4) It results that there are three species of Mesonyx : M. ossifragus 

 Cope, M. lanius Cope, and M. ohtusidens Cope. 



4^. ossifragus was the largest Creodont of the Eocene, equaling tlie 

 largest grizzly bear in the size of its skull. In a cranium with lower jaw 

 and almost complete dentition, the length to the premaxillary border from 

 the postglenoid crest is M. .365 ; the largest Ursus horribilis in my collec- 

 tion gives .270 for the same length. This specimen has the dental formula 

 I. I ; C.\; P-m.|; M. f . The claws have the flattened form which I 

 discovered in M. lanius, and the proximal phalanges have much the shape 

 of those of a Perissodactyle. Tlie astraglus has much the character of the 

 animals of that order, and has the distal facets as I originally detected 

 them in the M. oUusidens. The form of this bone is rather shorter and 

 wider than in the latter species. 



The inferior canine tooth of a large specimen has the following diameters 

 at the base of the crown : anteroposterior .039 ; transverse .024. 



AMBLYPODA. 

 Pantodonta. 

 The explorations in the bad lands of the Big-Horn river yielded several 

 species of this sub-order, all which I refer at present to the Coryphodontidm. 

 They, however, represent several genera, two of which have not been 

 previously known. I have distinguished these (American Naturalist, Jan., 

 1882), in the characters of the superior molar teeth as follows : 



I. Last superior molar with two interior cusps. 



All the superior molars with a well marked external posterior V 



Manteodon. 



II. Last superior molar with but one inner cusp or angle. 

 a. Last superior molar with posterior external cusp. 



Anterior two molars with posterior external V Ectacodon. 



aa. Last superior molar without external posterior cusp, 

 f Anterior two molars with posterior external V. 



Astralagus transverse, with internal hook Corypliodon. 



Astragalus subquadrate, without internal hook Bathmodon. 



ff First superior molar only with posterior external V Mctalophodon. 



