GEOLOGICAL SUEVEY OF THE TEERITOEIES. 363 



curves inwardly to tbe 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. 



Hyoiisodus pmdus. 



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- 

 l)ied by the molar series, 11 lines ; by the true molar series, 5f 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 beloug to another small joachyderm, to which I gave 

 the name of Microsus cusindatus, 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. 



MiCEOSYOPS. 



Microsyojps gracilis. 



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

 is indicated by several lower-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, 

 I)robably of the same animal, though it is not improbable they may per- 

 tain to Hyopsodus pmilus. 



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 lines 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 smailler, compared with the outer ones, than in Hyopsodus. Of the 

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

 terminates 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 one ends at the bottom of the lobe in advance, and the 

 back one terminates in a tubercle behind the interval of the posterior 

 pair of lobes of the crown. The depth of the jaw at the middle true 

 molar is 4^ lines. 



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

 he refers to a species with the name of Hyopsodtis gracilis. These I sus- 

 pect 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 Microsyops 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 5^ lines in another. 



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

 tinct equine genus Anchitherium. The last premolar resembles that of 

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

 inserted with three fangs. The first premolar of the specimen was in- 

 serted by a pair of fangs. 



