Cope.] **VA [Jan. 5, 1883. 



nal cusp, which has a semicircular section. The large anterior cusps are 

 confluent on wearing. No anterior cingulum in the worn crown. The 

 crowns of the first and second true molars of the specimen are rather worn. 

 They show that the posterior median tubercle is very indistinct and prob- 

 ably absent. The bases of the smaller inner cusps are round, and on wear- 

 ing unite with the larger external cusps. Of the latter the posterior is the 

 larger. Anterior cingulum rudimental or wanting. No lateral or pos- 

 terior cingula. The principal peculiarity of the lower dentition of this 

 species and the one from which it is named, is the form of the third or 

 fourth (probably third) premolars, both of which are preserved. They 

 have a compressed apex, which descends steeply to the anterior base, with- 

 out basal or lateral tubercle. The base of the crown sprsads out laterally 

 behindhand is broadly rounded at the posterior margin, so as to resemble 

 the toe of a wide and moccasined foot. It is depressed, the surface rising to 

 the apex from a flat base. * 



, Measurements. M. 



Diameters of seeond superior molar \ ^SSSS^. \ S 

 Diameters of las. superior molar \ jj™^*-— ijgg 

 Length of inferior true molars 0258 



Diameters of M. ii \ anteroposterior 009 



£ transverse 008 



Diameters of H. m{^S^ :;:::::::::::::::: : j«J 



Diameters of the P-m. m{fSSS^\::":""^ X 



About the size of the P. puercensis. 



Note on the Mammalia op the Puerco and the Origin of the 

 quadrituberculate Superior Molar. — It is now apparent that the type 

 of superior molar tooth which predominated during the PuerCo epoch 

 was triangular; that is, with two external, and one internal tubercles. 

 Thus of forty-one species of Mammalia of which the superior molars are 

 known, all but four have three tubercles of the crown, and of these thirty- 

 eight triangular ones we may except those of three species of Periptychus, 

 which have a small supplementary lobe on each side of the median prin- 

 cipal 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 Insectivora, and the 

 tubercular molars of such Carnivora as possess them (excepting the planti- 

 grades). In the Ungulates the only traces of it are to be found in the 

 molars of the Coryphodontidae of the Wasatch, and Dinocerata of the 



