Cope.] 324 [Dec.7, 
8. In no species of this formation is the fourth inferior premolar like a 
molar tooth. 
It is thus evident that the dentition of the mammalia of the Puerco 
fauna presents a much greater degree of simplicity than does that of the 
species of any of the later Hocene or other age. This result coiacides 
with the results I have already obtained from a study of the structure of 
the feet, etc.* These may be summarized again as follows: 
1. The species in which the number of toes is known, have them 5-5. 
2. Those in which the feet are known are plantigrade. 
8. No species is known to have interlocking carpal and tarsal bones, 
excepting the two species of Puntolambdu (carpus unknown). 
4. No species is known to have well grooved astragalus (its presence is 
inferred in two species of Dissacus). 
5. No species is known to have a faceted radius or ulno-radius, adapted 
to the separate carpal bones of the proximal row. 
6. Inno species is the tongue in the metapodio-phalangeal joints devel- 
oped on the front of the metapodial bones. 
Y. The zygapophyses where known are all flat, except in some species 
(probably all) of Oxyclenus, where they are simply convex-concave, and 
not doubly so. 
On the Trituberculate Type of Molar Tooth in the Mammalia, By H. D. 
Cope. 
(Read before the American Philosophical Society, December 7, 1583.) 
It is now apparent that the type of superior molar tooth which pre- 
dominated during the Puerco epoch was triangular or tritubercular ; that 
is, with two external and one internal tubercles. Thus, of sixty-seven 
species of placental mammalia of which the superior molars are known, 
all but four have three tubercles of the crown, and of the remaining sixty- 
five, all are triangular, excepting those of three species of Periptychus, and 
three of Conoryctes, which have a small supplementary lobe on each side 
of the median principal inner tubercle. 
This fact is important as indicating the mode of development of the 
various types of superior molar teeth, on which we have not heretofore 
had clear light. In the first place, this type of molar exists to-day only in 
the insectivorous and carnivorous Marsupialia ; in the Creodonta, and the 
tubercular molars of such Carnivora as possess them (excepting the plan- 
tigrades). In the Ungulates its persistence is to be found in the molars of 
the Coryphodontids of the Wasatch,and Dinocerata of the Bridger Hocenes. 
In later epochs it is occasionally seen only in the last superior molar. 
It is also evident that the quadritubercular molar is derived from the tri- 
tubercular by the addition of a lobe of the inner part of a cingulum of the 
* American Naturalist, 1888, p. 1056; Science, 1888, p. 275. 
+See American Naturalist, April, 1883, p. 407. 
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