1889.] 4ol [Cope. 



HiPPOTHERIUM CALAMARIUM Cope. 



Annual Report of U. S. Chief of Engineers, 1875, ii, p. 990. Report U. 

 S. G. G. Survey W. of lOOlli Mer., G. M. Wheeler, p. 331, PI. Ixxv, 

 Figs. 1-2. 



With this species we enter the group characterized by the general equal- 

 ity in size and form of the anterior and posterior internal columns of the 

 superior molars, and the presence of a rudiment in the anterior column, 

 of an isthmus corresponding with that one which connects the posterior 

 inner column with the posterior inner crescent. 



The H. calamarium has been found especially abundant in the Loup 

 Fork bed of Pojuaque near Santa Fe, New Mexico, and I have a portion 

 of a maxillary bone supporting two molars, from the corresponding hori- 

 zon of Northeast Colorado, which may be placed here provisionally in the 

 absence of the third superior premolar. The borders of the lakes are of 

 medium complexity only, and the posterior loop of the anterior lake is 

 rounded, and is not much constricted. The anterior inner crescent of the 

 third (anterior) premolar is isolated. Tliis tooth differs from the corre- 

 sponding one of the H. sphenodus and the H. isonesum in its short, wide 

 form. Should the latter character be found not constant, I do not know 

 of any way of distinguishing it from the latter. In the former the poste- 

 rior internal column is less prominent and smaller, much as in H. specio- 

 8um, etc. Cementum layer thick. Crowns nearly square, short, curved. 



Measurements of Specimen from Colorado. 



MM. 



Diameters of m. i 



anteroposterior 24 



transverse 24 



HiPPOTHERIUM ISONESUM Cope. 



Hippotherium seversum Cope, Proceeds. Amer. Philos. Society, 1886, 359, 

 not of 1878, p. 76. 



Judging from the relative abundance of specimens, this was the common 

 species of the far Northwest of the United States during the Upper Mio- 

 cene period. I have the large part of a skeleton with skull from Cotton- 

 wood creek, Oregon ; parts of maxillary bones with teeth of a second 

 individual from the same locality, with some teeth of a third from the 

 same. There are a good many teeth of the same species from the Ticho- 

 leptus bed of the valley of Deep river, Montana, a number of which be- 

 long to one individual. 



In the subequal characters of the two inner columns of the superior 

 molars, the species betrays an approach to Protohippus, which is empha- 

 sized by the angular projection of the anterior column towards the ante- 

 rior internal crescent. The two however never join, and only come into 

 contact in one instance, in the third premolar of a Montana specimen. 



