30 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 72 



withdraw. The number of vertebrae also varies in a quite capricious 

 manner. 



One of the most primitive Delphinids is no doubt the Tertiary 

 North American Delphinodon, the skeleton of which is known rather 

 completely. In comparison with its various relatives it has the 

 following primitive peculiarities. The teeth are present in large 

 numbers. They are small and nearly simply conical, some of them, 

 however, with wrinkles or small projections on the base of the crown, 

 probably mementos of the crown's formerly serrate margins and of 

 its also otherwise less simple form. The facial part of the skull is 

 rather long and narrow. As in the related forms which are lowest 

 in this respect the anterior end of the intermaxillary was probably 

 freely projecting, tooth bearing, and not grown over by the maxillary. 

 The upper margin of the intermaxillary does not come in contact with 

 its fellow. The symphysis menti is long; nasal slightly projecting; 

 cervical vertebrge distinct. It shows a peculiarity of its own in having 

 a longitudinal crest on the projecting lateral part of the basioccipital. 



The Tertiary European Champsodelphis (judging chiefly from 

 Ch. ombonii, Acrodelphis) presumably stands near to Delphinodon. 

 It is known from scarcely anything else than scanty remains of the 

 skull. It shows high specialization in the modification of the rostrum 

 to serve as an implement for boring or rooting in the sea bottom. 

 The facial part of the skull has acquired an unusual length and 

 slenderness ; the teeth have probably disappeared from the inter- 

 maxillary, and the upper margin of this bone was probably in contact 

 with its fellow through a considerable part of its extent. 



The Tertiary European Schizodelphis (judging from vS. sulcatus, 

 Cyrtodelphis) , also known practically from the skull only, must be a 

 near relative of Champsodelphis with which it appears to have most 

 of its peculiarities in common, both the primitive characters and the 

 special modifications. Its most important difference appears to be 

 that its teeth have gone still further in the direction of simplicity ; 

 the only reminders of earlier, less reduced form that have remained 

 behind are a slight widening out of the crown's base, which may be 

 found on some of the teeth, and the trenchant character of its anterior 

 and posterior margins. 



The Tertiary European Hcterodclphis, which is known from rather 

 considerable parts of the skeleton, undoubtedly stands close to Schizo- 

 delphis. Its teeth have become still more simple, with purely conical 

 crowns. 



