38 SMITHSOXIAX MISCELLANEOUS COLLECTIONS VOL. 72 



in the posterior nasal passage and in the facial bones becomes more 

 conspicuous than in other whales. The resistance of the water has 

 acted upon the skull in other ways also, different in the different 

 groups ; there is a tendency toward strengthening and coalescence of 

 the bones of the face, toward the appearance of projecting osseous 

 protuberances, etc. 



The members of the family, so far as they are known in this 

 respect, show a peculiarity in the relation between the ribs and the 

 transverse processes on the posterior thoracic vertebrae, in which they 

 form a contrast to at least the living forms of Delphinids. While in 

 the Delphinids the hinder ribs apparently lose the capitulum and 

 retain the tuberculum (the most posterior, probably having their own 

 history, have never had more than a single head), in the Physeterids 

 it is the tuberculum that disappears, while the capitulum remains. 

 On one or two of the hindmost ribs it may happen that the capitulum 

 and tuberculum can be seen at the same time, each in contact with its 

 " transverse process " ; but the tuberculum with its corresponding 

 process, a diapophysis, is in course of atrophy." 



The genera of the section Xiphiini stand lowest. In them the 

 occipital wall, which forms the posterior margin of the facial depres- 

 sion, is highly elevated in a section at the middle only, behind the nares, 

 and is not pushed very far back in relation to the nares. In the con- 

 trasted Physcterini the occipital wall is heightened through its whole 

 extent and more pushed backward. Likewise a primitive feature of 

 those Xiphiines that are known in this respect is that a more or less 

 distinct lacrimal bone is present, though in an atrophied condition, 

 spreading out especially in the roof of the orbit. 



The essentially most primitive genus of the Xiphiines is no doubt 

 the Tertiary South American Argyrodelphis (Notocctus, Diochoti- 

 chus), of the group Argyrodelphini, not known from much else than 

 the skull. It stands lower than all other known Physeterids in having 

 a relatively robust and arcuate zygomatic process of the squamosal 

 and in the character of the dentition. There is a long row of small, 

 well-developed, conical teeth in both upper and lower jaw, some of 

 them bearing notches on the margin of the crown. On the contrary, 

 as compared with one or another of the other genera, it is advanced 

 in having the occipital wall pushed rather far back, in having a rather 

 large cushion-shaped outgrowth on the maxillary above the orbit, and 

 in having the intermaxillaries spread inward over the mesethmoid 

 and coming into mutual contact with age. The cervical vertebrae 

 were free. 



