506 The American Naturalist. [June, 



Cymbella lanceolatum Ehr. ; Denticula valida Pediceno ; Epithemia 

 gibba (Ehr.), Kutz ; Epithemia gibba var. parallela Grim ; Epithemia 

 zebra Ehr., Kutz; Epithemia gibberula (Ehr.), Kutz var. producta 

 Grim; Epithemia constricta Breb ; Encyonema ventricosum Kutz; 

 Gomphonema elavatum Ehr.; Fragillaria virescens Ralfs. ; Navicula 

 major Kutz ; Navicula viridis Kutz ; Navicula rostrata Ehr. forma 

 minor; Navicula bohemica Ehr.; Navicula elliptica var. minutissum 

 Grim ; Navicula decurrens ; Navicula varians Greg. ; Navicula brebis- 

 sonii Kutz; Navicula forma Km/: Xltzschia brebissoiiiaWsm.; Nitz- 

 schia spectabilis (Ehr.), Ralfs. ; Surrirella geroltii var.— Lewis Wool- 

 man and C. Henry Kain. 



In the paper previously referred to Prof. Cope notes the occurrence 

 in this diatomaceous stratum of a " Mastodon of the angustidens 

 type " and of a horse allied to the Equus ocidentalis of Leidy, and 

 defines the latter as a new species to which he assigns the name Equus 

 simplicidens ; and indicates by a comparison of Equus and Mastodon 

 fauna that the age of the Blanco Canon beds is probably intermediate 

 between that of the Equus beds and the Loup Fork beds or the 

 equivalent of the pliocene proper. 



In view of this determination of the age of these beds the close cor- 

 respondence of all the specific forms of diatoms above listed becomes 

 interesting as showing the wide geological range for the forms of these 



Is Meniscotherium a Member of the Chalicotheriodea ?— 

 The description of the complete foot structure of Meniscotherium or 

 Hyracops by Marsh 1 tends to confirm the supposition I advanced in 

 the Naturalist of October, 1891. At the time, I stated that the 

 structure of the skull and teeth of Meniscotherium pointed to a striking 

 similarity between this Wahsatch genus and the Miocene Chalico- 

 therium, but that the question would turn upon the foot structure of 

 the earlier form. 



I reproduce here, side by side, for purposes of comparison, the fore 

 and hind feet of Meniscotherium (Hyracops) sociale Marsh, and of 

 iitm, from the figures of Gervais. 



It will be seen at once that both are essentially tridactyl types. In 

 Meniscotherium the three middle digits are greatly enlarged while the 

 outer digits I and V are equally reduced in both the manus and pes, 

 indicating that the feet are well established upon the tridactyl basis. 

 Marsh describes the ungual phalanges, as intermediate between hoofs 



