OF THE WHITE RIVEK BEDS OF MONTANA. 2t>'6 



This species is much smaller than E. elegans Leidy. The mental foramen is near 

 the upper border of the diastema and apparently much in advance of the middle. The 

 anterior angle of the masseteric area is under the anterior molar. Both teeth are some- 

 what worn on their grinding surfaces. Their antero-posterior diameters are nearly 

 equal, but the second is broader transversely than the first. The anterior part of the 

 first molar (cheek tooth) is not plainly divided into two lobes, but is subcorneal with a 

 pit in the middle of the truncated apex. Its transverse is greater than its antero- 

 posterior diameter. It is not much worn. It is smaller than the posterior portion of the 

 tooth, in which there is a posterior outer tubercle, from which three slender lobes extend 

 inward. The anterior lobe is the longest and the posterior the shortest. The second 

 tooth has the two rounded outer tubercles and live slender inner lobes. It looks as if 

 each outer tubercle sent in three inner lobes, but the contiguous two unite to form one 

 median one. On looking at the grinding surface, it is not easy to make out the four 

 principal lobes as it is in Leidy's figure of a tooth of E. elegans (1869, PL XXVI, 

 Fig. 13). On examining the tooth from the inside it is seen that, beginning anteriorly, 

 the second lobe forms the large anterior inner tubercle and the fourth the posterior one. 

 The first and fifth arc accessory, and the third is in the median valley between the two 

 tubercles. It seems that a little further wear would unite the two anterior lobes. 



Measurement*. 



Depth of jaw al mental foramen 00 ' 



Depth under second molar 00t ' 



Thickness under second molar 00 '"' J 



on ' r i 



Length of first molar UU1U 



Width of lii-st molar 0013 



Length of second molar 



,,,.,',,,, , , ,,. 0017 



Widili ol second molar 



Hycenodon monlauus, sp. nov. 

 Type No. 40. 



A portion of a skull and mandible with all the teeth represented except the lower 

 incisors. Found northeast of Toston, a, village on the Missouri river, southeast of 

 Helena,. This was the only fossil secured from this stratum ; but teeth of two species 

 of Colodon were found in lower strata. The skulls of Oreodon robustum, 0. eulbert- 

 soni (?), and Eucrotaphus helenas were found farther to the northeast, but I am not sure 

 whether the beds are higher or lower. 



Larger than //. crucians; crown of upper canine nearly straight ; crown of P 2 high 

 and without posterior cusp; talons on P ¥ and P T , but not on P Y . 



A. P. S. — VOL. XX. (!<i. 



