420 F. B. Zoom is — Hyopsodidce. 



Locality — 27 specimens were collected from both the upper 

 and lower beds of the Wasatch on Gray Bull River. 



They run very uniform in size, the length of the three lower 

 molars being between 10 and ll mm . In a few cases the last 

 lower molar was considerable smaller than the normal. 



Hyopsodus miticulus Cope.* 



This form from the New Mexico Wasatch is thus described 

 by Cope : " Parts of several specimens of this species show 

 that the molars are similar in size to H. paulas, but that it has 

 a much smaller last inferior molar, which has such a low heel as 

 to resemble the corresponding tooth of the species of EstlionyxP 



The species seems to resemble H. simplex most, but is larger 

 and differs in the heel being low, and more developed. The 

 last molar is also proportionally smaller. The two cannot in 

 the writer's opinion be included in one species. 



Hyopsodus lemoinianus Cope.f 



This species presents several difficulties on account of the 

 large amount of variation in size, and in the development of 

 both the metaconid and the metalophicl ; but in as much as 

 these variations do not seem to be constant, and as interme- 

 diate forms are found between the widest variations, all these 

 related forms have been assigned to the one species. H. lemoin- 

 ianus was established by Cope, who figured a left ramus with 

 the molars, on which the metaconid is but slightly bifid. 

 Osborn figures a second specimen with the metaconids also but 

 little twinned. Most of the Amherst specimens have this cusp 

 markedly bifid, as is seen in the specimen figured. 



The species may be described as follows : 



^C\ ^W^ There is a cingulum on the front of the 



^H BIB |v tooth, and between the external cusps of the 



moderately stout teeth. On molars one and 



two, there is developed on the inner end of 



the protolophid a small but distinct paraconid, 



which makes the metaconid appear bifid. The 



.d^iLSSE metalophidis either entirely wanting or but 



X f. moderately developed. Iheentoconid is small, 



as is also the hypoconulid. The last lower 



molar is longer, and similar except that the hypoconulid is 



developed into a prominent heel. On the upper molars the 



cingulum is well marked and the cusps fairly high. 



The three lower molars measure 13 to 15 mm , there being con- 

 siderable variation in size. The nine specimens collected all 

 occurred in the basal beds along the Gray Bull River, Wyoming. 



* Rep. Vert. Fossils of New Mexico, Appen. F.F., Rep. Chief. Eng., 8, 1874. 

 fProc. Amer. Phil. Soc, xx, 148, 1881. 



