24 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 72 



in the upper jaw 12, cheekteeth. Of these last the four or five 

 anterior have conical crown and single or bifid root, and the seven 

 posterior have compressed crown with more or less serrate anterior 

 and posterior margin (or only the posterior margin serrate), and 

 two roots, an anterior and posterior. The fact that the number of 

 cheekteeth is most often 11 might indicate that the increase above 

 the typical number, seven, was produced by the intercalation of four 

 milkteeth in the series with the seven permanent teeth ; but there is 

 no decisive evidence either for or against this explanation, as the tooth 

 succession is not known. If the number exceeds 11 a true increase 

 must have taken place. As in the most primitive of the higher whales 

 the jaws are very elongate, narrow ; the intermaxillary and maxillary 

 are not especially closed together, and the mesethmoid is not ossified 

 in front ; the symphysis menti is long (the rami of the mandible may 

 have grown together) ; the facial depression does not extend very far 

 backward, the braincase is relatively only a little telescoped, the 

 temporal fossa is considerable, the zygomatic process of the squamosal 

 strong, the occipital condyle projecting. 



The Tertiary European Neosqiialodon is only known from pieces 

 of jaws. It has the number of serrate cheekteeth raised to at least 

 II ; otherwise the characters of the dentition are not known. 



The Tertiary Argentinian Prosqualodon, known from the more 

 essential parts of the skull, differs from Squalodon in having a much 

 shortened face, with the facial depression relatively strongly broad- 

 ened behind. The number of teeth appears to be somewhat reduced. 

 It is no doubt a little more primitive than Squalodon in the less 

 strongly telescoped form of the braincase proper. 



Squalodontidae.'' 



I. Braincase only slightly telescoped. 



Agorophius. 

 II. Braincase strongly telescoped. 



A. Face long. 



1. Number of cheekteeth relatively little increased 



above the typical [44]. 

 Squalodon. 



2. Number of cheekteeth increased above the typical 44. 



Neosqualodon. 



B. Face shortened. 



Prosqualodon. 



