20 DIXOCERATA. 



ligaments which supported the head. Tlie lofty occipital crest extends 

 upward and backward, overhanging- the occipital condyles, when the 

 skull is in a horizontal position. The posterior margin of the large 

 temporal fossa also extends well backward, forming the side of the 

 occipital concavity, which is partially divided into two equal portions by 

 a median vertical ridge. In some species, this ridge is very distinct, but, 

 in others, it is almost entirely wanting. 



Tlie occipital condyles are large, and bounded externally in front 

 and below by a deep groove. They project downward and backAvard, 

 showing that the head was declined when in its natural position. 



In Dinoceras laticeps (number 1039), the occiput is less elevated, and 

 more expanded transversely, figure 14, page 19. Its concavity is divided 

 into two portions by a distinct median vertical ridge. The foramen 

 magnum, also, is expanded transverselv, and is of moderate size. The 

 occipital condyles are more elevated than in Dinoceras mirahile, a line 

 joining their upper margins passing entirely above the. foramen magnum. 



In Dinoceras agrcste (number 1221), a third type of occiput is seen, 

 much more expanded aliove, as shown in figure 15, page 19. Tlic foramen 

 magnum is here subtriangular in outline, and the occipital condyles are 

 placed similarly to those of Dinoceras iirirahile. 



In the genus Tinoccras, two distinct types of occiput are represented 

 in the Yale Museum. In Tinoccras iiafrns (number 1041), the occiput is 

 greatly elevated, somewhat concave above, and expanded at tlie sides. 

 There is no median crest. The foramen magninn is triangular in outline, 

 and comparatively small, witli its uj)j)er border lower tlinn the superior 

 margins of the occipital condyles, as seen in figure 17, i)age 19. 



In Tinoceras 2^ugnax (number 1044), the occiput is less elevated, and 

 more nearly cpiadrate in outline. The foramen magmun is large, and 

 transversely expanded. The occipital condyles extend above its upper 

 margin, as shown in figure 18, page 19. In other species of the 

 Dinoccrafu, the occiput shows an equal variety of forms. 



In Dinoceras mirahile (number 1036), there is a small, but distinct, 

 par-occipital jjrocess of the ex-occipital, directed downward and outward. 



