NO. 8 INTERRELATIONSHIPS OF THE CETACEA WINGE 3I 



In the Tertiary European Eiirhinodelphis, which is known from 

 most of the skull and from parts of the rest of the skeleton, the 

 transformation of the snout into a rooting implement has reached the 

 highest limit. The rostrum, both upper jaw and lower jaw, has 

 grown forward anteriorly as a long slender point, still more notice- 

 ably than in any of the other genera. The intermaxillary has ex- 

 tended itself, awl-shaped and toothless, far forward beyond the 

 maxillary. The tip of the lower jaw appears to be formed in a corre- 

 sponding manner. The teeth are simply conical. 



No doubt the Tertiary South American Argyrocetus is very nearly 

 related to EurhinodelpJns. It is known from a defective skull, and 

 appears to differ in trifles only. 



The genera just mentioned of the group Eurhinodelphini form a 

 contrast with the group Monodontes. The latter includes the genera 

 Delphinapterns and Monodon, which must have originated from the 

 oldest Eurhinodelphines in which the tip of the snout had not been 

 remodeled as a rooting implement. In common with the Eurhino- 

 delphines (at least with Delphinodon, Heterodelphis, Eurhinodelphis, 

 and Argyrocetus, which are known in this respect) the Monodonts 

 alone among the Delphinids have the primitive character that the 

 cervical vertebrae are mutually independent. Other indications of 

 low origin seem to be shown by the Monodonts in the form of the 

 teeth (in which one of the genera may recall Delphinodon and 

 others), in the decidedly short spinous and transverse processes of 

 the thoracic vertebrse, in the relatively short fingers, and perhaps also 

 in the absence of the dorsal fin. But in the flat and broad form of the 

 face, probably resulting from their habit of not using the jaws for 

 much else than to clap together on tender cuttlefish, the Monodonts 

 are more highly developed than their progenitors among the Eurhino- 

 delphines. The same is true of their lack of the olecranon." 



The most primitive of the known Monodonts is Delphinapterus. 

 It shows its primitiveness in relation to its nearest ally by its rather 

 ordinary dentition : the teeth are present in relatively considerable 

 numbers, about lo in each jaw; they are small and conical, but in the 

 upper jaw they are directed forward in a peculiar manner. The 

 teeth have disappeared from the intermaxillary. 



In Monodon the teeth, with a single exception, are in process of 

 atrophy and disappearance; only a few of them are present in the 

 young. One of the foremost teeth in each maxilla has had its peculiar 

 destiny : it has grown forward as a " ramming-tooth," at first no 

 doubt uniformly in the right and left jaw and in the male and female, 



