HYRACOTHEEIUM. 649 



an anterior basal cingulum. There is no trace of the inner posterior cusp 

 which is seen in the genus Pliolophus. External cingulum scarcely a trace. 

 Enamel nearly smooth. In the true molars the anterior ledge and posterior 

 median tubercle are little developed; the oblique ridges are well developed, 

 and the heel of the last molar elevated. The molars have a strong cingu- 

 lum on the outer side, and the enamel is slightly rugose. The ramus is 

 slender. 



Measurements of a New Mexican specimen. 



Length of the bases of three true molars 0.024 



Length of the penultimate molar 0.007 



Width of the same 0.005 



Depth of the ramus at the last molar 0.0125 



\ 



The variations from the above standard of measurement found in the 

 Wind River specimens are as follows. There are three sizes which may 

 represent different species, but this cannot be determined without better 

 material : 



A. Depth of ramus at last premolar or first true molar, .0130; length 

 of crown of first true molar, .0070; length of last true molar, .0100. 

 Lower jaw of one specimen. 



B Depth of ramus, .0140; length of first true molar, .0065; of last 

 molar, .0100. One lower jaw. 



C. Depth of ramus, .0155; length of first true molar, .0075; of last 

 true molar, .0100. Two individuals. 



Portions of lower jaws of three other individuals in the Wind River 

 collection are apparently referable to the H. angustidens. Variety A was 

 obtained in the Big Horn basin north of the Wind River, by Mr. Wortman. 

 The majority of the Big Horn specimens agree with the variety B, but two 

 others occur, one a little smaller and the other a little larger than the aver- 

 age. The former measures: length of last molar, .0090; of first molar, 

 .0067; depth of ramus at M. i, .0120. The dimensions of the larger variety 

 are: length of M. iii, .110; of M. i, .0067; depth of ramus, .0165. The 

 New Mexican forms originally described exhibit combinations of several of 

 these measurements. 



