Cope.] 44b pjay 3, 



The mandibular rami which probably belong to this species present tlie 

 character of an uninterrupted series of canine and incisor teeth. The 

 symphysis is contracted, and the rami increase rapidly in depth. The 

 diastema is long. No trace of fourth premolar. 



Measuremen's. 



MM. 



Length of symphysis 37 



" " diastema 46 



Depth of ramus at posterior border of p. m. iv 40 



HirPOTHEKlUM RETRUSUM CopC. 



Tins species is represented in my collection by eight molars, two from 

 one and six from another animal. These are associated with two superior 

 molars with somewhat different characters, which are intermediate be- 

 tween those of H. gratitm and H. speciosiim. All were found in the 

 same locality, but separated from their positions in tlie skull. The two 

 molars first above mentioned are about half worn, and present the char- 

 acters of the species best. The other six (with one exception) are less 

 worn, and present a less complex folding of the enamel ))lates. Five of 

 them are from one side, and one (more worn) from the other side of the 

 jaws. 



The character by which the superior molars of the HlppotJierintn retra- 

 sum may be readily distinguished from those of all other species of the 

 genus, is the extraordinary posterior extension of the anterior internal 

 column, Avhich brings it first into contact with the posterior internal col- 

 umn, and then on greater wear unites the two by an isthmus. In the first 

 true molar the area of the column is in contact at its extremities with both 

 the posterior column and the anterior inner crescent, leaving a narrow oval 

 area (or lake) within it, cut off at both extremities. In the second molar 

 the column is only in contact with the posterior internal crescent, with 

 which it is united by an isthmus. In both the molars the posterior inner 

 column is well distinguished by the usual deep sinus from the posterior 

 inner crescent. The character above described is an exaggeration of what 

 is distantly approached by the last superior molar in some of the species. 



The complexity of the enamel border of the lake is of medium degree. 

 The anterior lake has on its posterior border a large more or less com- 

 pletely isolated wide loop. Exterior to it the adjacent borders of both 

 lakes are thrown into narrow anteroposterior folds. No fold on remote 

 border of anterior lake, and a weak one at the corresponding position on 

 the posterior lake. A short small loop towards the internal column on 

 m. ii. The crowns are robust, of medium length, and curved. That of 

 the second true molar is rather longer than wide ; the first true molar is 

 about as wide as long. 



