68 



THE QUARTERLY REVIEW OF BIOLOGY 



porpoises, the conclusion can not be 

 avoided that they represent stages through 

 which some of those now living have 

 passed. The Calvert porpoises, Delphin- 

 odon dividum (True, 1912.) and Kentriodon 

 pernix (Kellogg, 192.7), resemble some of 

 the smaller living porpoises rather closely, 

 and it is not unlikely that they were as 

 active and as graceful as any of the living 

 types. 



Ant. tt. 



S. or. pr. 



transverse crest of the supraoccipital, 

 extremity of rostrum formed by the 

 premaxillaries and at least three teeth im- 

 planted in each of these bones, 40 teeth in 

 each upper jaw and 38 in each mandible. 

 The crowns of the teeth are recurved, 

 with relatively smooth enamel, but with 

 neither carinae nor accessory cusps; the 

 roots are slender, slightly enlarged below 

 the crown, and have a small pulp cavity. 



^S.onpr. 



S.'oc. ^ """ S - oc - 



Kentriodon pernix Delphinodon dividum 



Fig. 10. Dorsal Views of Skulls 

 Kentriodon pernix, Middle Miocene, Maryland. Delphinodon dividum., Middle Miocene, Maryland 



There is a marked resemblance between 

 the extinct Miocene Kentriodon -pernix and 

 the living southern porpoise Sot alia tucuxi. 

 The skeleton of Kentriodon is approxi- 

 mately 5! feet long. Its telescoped skull 

 has a short and narrow braincase, a 

 slender rostrum, a small, more or less 

 pentagonal vertex, the posterior extrem- 

 ity of the maxillary in contact with the 



Sotalia on the other hand lacks the 

 tusk-like teeth at the extremity of the 

 jaws; no teeth are implanted in the 

 premaxillary, for it does not project 

 beyond the maxillary; the braincase is 

 more expanded; and the maxillary has 

 receded from the crest of the supraoccipital. 

 As compared with Kentriodon, the skull 

 of Delphinodon dividum has a large, broad 



