12 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. ']2 



lower jaw, and from a few vertebrae and ribs. In all that is known it 

 stands so near to the HycBnodontidcB that there would scarcely have 

 been any reason to separate it from them had it not been evident that 

 it was one of the first members of the cetacean series. The number 

 of teeth in the upper jaw is, as in Stypolophus and Pterodon, the 

 typical II, since m^ is present, while it has disappeared in Hycenodon, 

 the highest genus of Hyccnodontidce. But the form of the teeth is 

 most nearly as in Hycenodon, more shearing than in other members 

 of the family. The difference from Hycenodoii is chiefly a result of 

 the fact that heavier use has been made of that part of the toothrow 

 which serves for grasping the food and that consequently the incisors 

 and anterior cheekteeth have increased in size. The incisors have 

 become about as heavy as the canine, the premolars have become 

 heavier and more elongated than formerly, while the molars are 

 weakened and m^ has lost its predominance. The mouth was already 

 used mostly as a pair of forceps ; the long, narrow, but strong, beak- 

 shaped jaw, in which the teeth have abundant space, bears witness 

 to the fact. The anterior nasal aperture is already forced consider- 

 ably backward; but it has, however, only reached a point scarcely 

 half way to the anterior margin of the orbit, and it has kept a rather 

 primitive form. The nasal bone is long and narrow, roofing over a 

 large part of the nasal cavity. The intermaxillary is strengthened 

 anteriorly, its body is lengthened, likewise its nasal process, though 

 this process does not reach to the frontal. Otherwise the inter- 

 maxillary does not show much deviation from the conditions ordi- 

 narily found in carnivores. The maxillary also is lengthened and 

 thickened; but is not otherwise modified to any noticeable degree. 

 Posteriorly it does not push itself out over the facial part of the 

 zygoma or over the frontal, which it merely forces slightly backward. 

 On the palatal surface it has not crowded the palatine bone, which 

 has retained its original length. The incisive foramina seem to have 

 disappeared. The forehead is pressed quite flat, and the supraorbital 

 process of the frontal has become very broad ; otherwise the forehead 

 is unmodified. The anterior and median part of the zygoma is 

 already well on its way to become slender, but the zygomatic process 

 of the squamosal is still robust. It bears a considerable postglenoid 

 process, though the articular surface for the lower jaw has begun 

 to assume the peculiar vertical position that it has in the higher 

 whales. The temporal fossa has on the whole remained primitive 

 in size and form. It is bounded by high crests. The braincase is 

 not compressed antero-posteriorly ; the frontal and supraoccipital are 



