CEEODONTA. 355 



is no internal tubercle, it is true, but the median tubercle is a cone, and 

 the anterior is rudimental, so that there is no sectorial structure. The 

 structure of the feet in Hycenodon being yet unknown, it is not possible to 

 state the relations seen in these parts. The hind feet ai'e, as already pointed 

 out, entirely different from those of other Creodonta, to which group the 

 fore feet refer the genus. The flat claws are a unique peculiarity, and 

 suggest affinity to the seals, and an aquatic habit. The teeth, moreover, 

 show a tendency in the same direction, in the simplicity of their crowns. 

 The structure of the ankle forbids the supposition that these animals were 

 exclusively aquatic, as it is of the type of the most perfect terrestrial ani- 

 mals. The reduced number of digits — four both anterio)"ly and posteri- 

 orly — as in the Hycenidoe, is also opposed to any suggestion of aquatic 

 habits. 



Species. Two are certainly known, and a third may be in our collec- 

 tions. The former are distinguished as follows, by the dentition of the 

 lower jaw : 



Smaller in aU dimensions, except in the first true molar, which is equal 



that of M. lanius M. obtusidena. 



Larger by one-half, except in the first true molar, which equals that of 



the other species M. laniua 



The specimen in the Princeton museum, already mentioned, is of simi- 

 lar form and proportions to the M. lanius, excepting that the last two 

 inferior true molai-s are only four-fifths as long as those of the S. lanius. 



History. I have been unable to find any reference to this genus othei 

 than those included in the citations at the head of this article. 



Mesonyx obtusidens Cope. 



Proceediugs American Philosopliical Society, 1872, 480 (July 29), et loc. Bup. cit. 

 Plate xxvi, figs. 3-12; xxvii, figs. 1-24. 



Of the typical specimen of this species, there are preserved portions of 

 the skull with teeth, chiefly mandibular ; numerous vertebrae from all parts 

 of the column ; parts of scapula, ulna, and fore feet, portions of pelvis, 

 femora, tibiae, tarsals, metatarsals, and phalanges. 



There are numerous teeth preserved, but separate from the skull and 

 mostly mandibular. The inferior canine is stout, especially in the root, 



