GEOLOGICAL SUEVEY OF THE TERRITORIES. 363 



curves inwardly to the base of the antero-internal lobe. The posterior 

 horn of the posterior crescentoid summit ends in a tubercle at the back 

 of the crown, opposite the" interval of the hinder pair of lobes. 



Hyopsodus patdus. 



The species was about the size of a Eabbit. Distance from the back 

 of the last lower molar tooth to the chin is about 13 lines. Space occu- 

 pied by the molar series, 11 lines -, by the true molar series, 5|- lines ; 

 and in another specimen, 6 lines. Depth of the lower jaw, from 3| to 4 

 lines. 



A lower-jaw fragment, containing the last pair of molar teeth unworn, 

 which I supposed to belong to another small pachyderm, to which I gave 

 the name of Microsus cuspidatus, I now suspect to belong to the same 

 animal as the former. The specimen was obtained by Prof. Hayden 

 at Black's Fork, of Green Eiver, Wyoming. The jaw is much more 

 slender than in the more characteristic specimens referred to Hyopsodus 

 paulus. Below the second true molar it is only 3 lines in depth, whereas 

 in the latter specimens in the same position it is 4 lines. Perhaps the 

 fragment may indicate another species. 



MlCROSYOPS. 



Microsyops gracilis. 



Another diminutive pachyderm, about the size of that just described, 

 is indicated by several low^er-jaw fragments, discovered last summer by 

 Dr. Carter, at Grizzly Buttes and Lodge-Pole Trail. The specimens were 

 accompanied with others, consisting of upper-jaw fragments with teeth, 

 X)robabiy of the same animal, though it is not improbable they may per- 

 tain to Hyopsodus paulus. 



Microsyops gracilis possessed larger canines, and one molar less to the 

 series of the lower jaw than the last-named animal. Of incisor teeth or 

 their sockets, no remains are preserved in the specimens. 



The molar series is scarcely 10 liues in length, and the true molars oc- 

 cupy a half an inch of the space. The crowns of the latter teeth, except 

 the last one, which has an additional lobe, are composed of four lobes, as 

 in Hyopsodus gracilis. 



The fore part of the crown of the first and second true molars is de- 

 cidedly narrower than the back part. The inner lobes are proportion- 

 ately smaller, compared with the outer ones, than in Hyopsodus. Of the 

 diverging' arms of the summit of the antero-external lobe, the front one 

 termiDa^tes in a tubercle in advance of the antero-internal lobe, and the 

 back one joins the latter. Of the diverging arms of the postero-external 

 lobe, the front on-e ends at the bottom of the lobe in advance, and the 

 l)ack one teriiiinates in a tubercle behind the interval of the posterior 

 l^air of lobes of the crown. The depth of the jaw at the middle true 

 molar is 4 J lines. 



Prof. Marsh has described some remains from Grizzly Buttes, which 

 he refers to a species Avith the name of Hyopsodus gracilis. These I sus- 

 X)ect belong to the same animal. 



The upper-jaw specimens alluded to at the beginning of this article 

 are of a size to accord with those referred to Micy^osyops gracilis. Six 

 upper molars occupy a space of three-fourths of an inch. The true mo- 

 lars occupy a space of 5 lines in one specimen and o.J lines in another. 



The crowns of the upper true molars remind one of those of the ex- 

 tinct equine genus Ancliithermm. The last premolar resembles that of 

 a Deer, having a two-lobed crown. It and the premolar in advance are 

 inserted with three I'angs. The first premolar of the specimen Avas in- 

 serted by a pair of fangs. 



