436 Wortman — Studies of Eocene Mammalia in the 



right lower jaw of a young adult, figures 83, 84, containing all 

 the molars and the three posterior premolars, in an almost 

 perfect condition. The second specimen is more fragmentary, 

 8 but the anterior portion of the 



ramus is sufficiently preserved to 

 show the roots of the anterior pre- 

 molars and the canine. 



The teeth agree so perfectly, both 



in measurements and structure, with 



Figure 84.— Sinopa rapax Leidy's type of S. rapax, that I 



^^£lfi£r t not Imitate to refer them to 



this species. Containing, as they 

 do, almost the entire lower dentition, including the last two 

 molars, it is possible to compare them with Cope's type of 

 Stypolojphus pungens, which is also a jaw fragment carrying 

 the second and third molars. The Marsh specimens agree 

 quite as well with the Cope specimen as with that of Leidy, 

 from which it is evident that all refer to one and the same spe- 

 cies. I therefore unite them under Leidy's name /Sinopa rapax. 

 The characters of the species, as revealed by these specimens, 

 are as follows : The first lower premolar is single-rooted and 

 separated from the canine and second premolar by short dias- 

 temata ; the second, third, and fourth are not spaced, but are 

 in contact ; the first molar is the smallest and the second is 

 slightly larger than the third ; the trigon of the first molar is 

 considerably less elevated than that of either the second or 

 third ; the heels of the molars are relatively wide and basin- 

 shaped, that of the third or last being noticeably smaller and 

 narrower than the others ; the edge of the rim surrounding 

 the heel is interrupted on its postero-external border by a 

 moderately deep notch, which, when seen from the outside, 

 gives the heel the appearance of being bicusped. 



There is also in the collection a fragment of an upper jaw, 

 which includes the fourth superior premolar somewhat dam- 

 aged and the first and second molars in fairly good condition. 

 I place the specimen in this category more by exclusion than 

 by any real evidence which it exhibits. The size of the teeth 

 corresponds very well with those of the lower jaw, and they 

 display just such characters as w r e should expect to accompany 

 the lower series above described. Their chief characters are 

 the following : The fourth premolar has a large internal cusp 

 and a well-developed blade-like postero-external cusp ; the 

 first and second molars are subequal, the internal cusps are 

 relatively large and lunate, the two primary external cusps are 

 well separated, and the antero-external angle of the second is 

 not produced into a cutting blade. I give the following prin- 

 cipal measurements : 



