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' 
i 
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7 
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1888. ] 63 
[Cope, 
that this description does not refer to the characters of the premolar teeth 
which really distinguish these forms from Dicotyles. I also find the tuber- 
cles of the molar teeth in numerous examples rather less distinct from 
each other than is the case in the Dicotyles torquatus. Nor do I find the pos- 
terior nares to advance between the molars in any of my specimens which 
are not broken, but, on the contrary, this orifice is generally posterior in 
position to that which it occupies in Dicotyles. Disregarding these dis- 
crepancies, Mr. Wortman and I attempted to redefine this genus,* so as to 
represent the characters of the species known to us. I am now, however, 
inclined to think that we were prematute in this endeavor, and that it is 
quite possible that we are yet unfamiliar with the true Thinohyus. Asan 
attempt has been made to define the genus by Marsh, the name will have 
to be retained, but we must await fuller descriptions both of the genus 
and of its typical species, before we shall be able to give it its proper place 
in the system. 
My specimens resolve themselves into two series, those which have three 
premolars in the upper jaw, and those which have four. I do not know 
of any specimen which has but three premolars in the lower jaw. The 
fourth premolar (first of the old nomenclature) of the superior series is a 
small tooth, and may be in some instances subject to irregularities. How- 
ever, I retain the two genera, and compare them as follows: 
Dicotylide with premolar teeth all different from true molars. 
Inferior canine received into a deep fossa of the upper jaw; canines sub- 
triangular in section ; three superior premolars............ Chanohyus. 
Like the last, but four superior premolars...............ss0s Bothrolabis. 
Canines with oval section, not received into a fossa of the upper jaw ; 
Hyotherium. 
It may be remarked of the John Day species, that there is no such ex- 
cess of development of the first superior incisor in them as is seen in 
Dicotyles, and especially in Hyotherium. Three are constantly present in 
each premaxillary bone; but each mandibular ramus may have two or 
three. 
In the following descriptions the notation of the premolars used by 
Kowalevsky and Schlosser has been adopted; viz: p. m. i is the next 
tooth to m. i. 
Lithographic plates of these species have been printed, but cannot be 
published owing to the change of organization of the U. S. Geological 
Survey. 
CHANOHYUS Cope. 
Proceeds. Amer. Philos. Society, 1879, p. 373. 
CHANOHYUS DECEDENS Cope, l. c. 
This species was established on a large fragment of the cranium, which 
includes the orbits and all anterior to it, excepting the dentigerous portion 
* Fourteenth Report of the State Geologist of Indiana, 1884, Part II, p. 17. Proceeds. 
Amer. Philos. Soc., 1887, p. 384, 
