626 THE EOCENE FAUNA. 



the smaller posttympanic. There is a sagittal crest. The hamular pro- 

 cesses are well developed. 



The infraorbital foramen is of medium size The incisive foramina are 

 large. There is an alisphenoid canal. The foramen anterior to its anterior 

 opening I take to be the rotiindum, and in front of the latter is a larger 

 foramen, probably the / orhitosphenoidale, but as I cannot find the optic 

 foramen anterior to it, it ma}' include the latter also. It is very probable 

 that the foramen ovale is not distinguished from the / lacerum anterius. The 

 / postglenokleum is distinct, grooving the posterior base of the postglenoid 

 process. There is no supraglenoid foramen, but there are two or three 

 postsquamosals. The / condyloideiim is quite distinct from the / lacerum 

 posteriiis. I cannot be sure that there is a postparietal foramen; two near 

 the proper location in H, ventkolmn appearing to be in the squamosal bone. 

 The mastoid, if present, is not enlarged into a fissure, as in various recent 

 genera. 



The symphysis of the mandible is coossified at maturity. The con- 

 dyle is well elevated and the coronoid process is produced. 



The cranial characters above enumerated are derived from skulls of 

 H. ventkolmn and H. craspedotum. The details are generally much like 

 those of Anchitherium (anceps), omitting of course the generic and family 

 characters, seen in the double-crested premolars in continuous series In 

 the absence of the supraglenoid foramen we see an approximation to types 

 of Perissodactyles other than those of the equine line. The following generic 

 characters in the skeleton are derived from the H. venticolum. 



Twenty vertebrae of one individual of H. venticolum are preserved ; of 

 these, three are cervicals, twelve are dorsals, and six are lumbars. The 

 axis has the cylindric odontoid of other primitive types, and the atlantal 

 facets are well separated There are no transverse or vertical foramina, 

 but the vertebrarterial canal is present. The paradiapophysis is acumi- 

 nate, and is directed backward. The spine is elevated, and is extended 

 both anteriorly and posteriorly. The third or fourth cervical is rather 

 elongate, and has the vertebrarterial canal. The transverse process is 

 extended both forward and backward, and each extremity is acuminate. 

 The articular faces of the centrum are weakly opisthoccelous, and are very 



