404 THE PUERCO EPOCH. 



cusps characteristic of Pheiiacodcnitidoe and ungulate mammals. These teeth 

 therefore resemble premolars rather than true molars. Before I was ac- 

 quainted with Hajjloconus, I provi.sionally referred this genus to the Creodonta; 

 the resemblance to Haploconus is, however, unmistakable. The ridging of 

 the enamel is also present in the milk dentition. 



Measurements of milk dentition. 



M. 



Length of crown of first molar 0113 



Width of crown of tirst raolar 006 



Elevation of crown of first molar (XHi 



Length of secouil molar Oil 



AViilth if second molar 00" 



Elevation of second molar 0065 



Depth of ramus at second molar 020 



The species was obtained by Mr. D. Baldwin from "below all the 

 Wasatch Sandstones," in the Puerco. 



Peeiptychus diteigonus Cope. 



Plate XXIII </; fig. 12. 



This rare species is known from a right mandibular ramus which exhibits 

 part of the symphyseal suture, with the alveoli of the molar teeth except 

 the first. The only well-preserved crown is that of the second ti-ue molar. 



The second true molar presents very peculiar characters, and the 

 mandibular ramus is shallower and thicker than in the two other species of 

 Peripfi/chus. The former has a wide external cingulum which is not present 

 in the other species, and there are only six cusps instead of seven. These 

 are peculiarly arranged. The anterior three are much as in P. rhabdodon, 

 the anterior inner being not quite so far internal as the posterior inner, close 

 to it and as large as the anterior external. The posterior three are a pos- 

 terior inner and posterior median as in P. rhabdodon, and a peculiarly placed 

 posterior external. This is not opposite the posterior inner, but is anterior 

 to such a position, and intermediate between the latter point and the one 

 occupied by the median tubercle in P. rhabdodon. It is as large as the an- 

 terior external tubercle. All these tubercles are conical and not connected 

 by angles or ridges. The position of the posterior external cusp leaves the 

 cingulum wide posteriorly, and near its edge develops some small tubercles. 

 There are also some small tubercles at other points on the edge of the crown, 

 but no other cingula. The enamel is not regularly ridged as in P. rahbdodon, 

 but has a rather coarse obsolete wrinkling-. 



