324 



[Dec 7, 



8. la 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 Eocene or other age. This result coincides 

 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. 



3. No species is known to have interlocking carpal and tarsal bones, 

 excepting the two species of Pantolambda (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. In no species is the tongue in the metapodio-phalangeal joints devel- 

 oped on the front of the metapodial bones. 



7. The zygopophyses where known are all flat, except in some species 

 (probably all) of Oxyclcerius, where they are simply convex-concave, and 

 not doubly so. 



On the Trituberculate Type of Molar Tooth in the Mammalia. By E. D. 



Cope. 



(Bead before the American Philosophical Society, Dec. 7, 18SS.) 



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 Coryphodontidse of the Wasatch, and Dinocerata of the Bridger Eocenes. 

 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, 1883, p. 1056; Science, 1883, p. 275. 

 fSee American Naturalist, April, 1883, p. 407. 



