6 4 



THE QUARTERLY REVIEW OF BIOLOGY 



This series includes porpoises with very- 

 long rostra, whose distal extremities are 

 edentulous, or if teeth were present they 

 were implanted in a dentary ligament 

 along the vestigial alveolar groove. A 

 somewhat damaged skull, nearly com- 

 plete mandibles, including most of the 

 symphysis, four cervical vertebrae and 



tion has been eliminated and the backward 

 rostral thrust has carried the maxillary 

 to the supraoccipital. The full comple- 

 ment of teeth exceeds zoo. The vertex is 

 limited to a narrow strip of the conjoined 

 frontals, into the anterior borders of which 

 the squared nasal bones have sunk. 

 Cabrera (19x6) has pointed out the great 



Max. 



-Zyg. 



-Zyg. 



— c. 



S.'oc. 

 Eurhinoddphis bossi 



Cyrtodelphis sulcatus Argyrocetus patagonicus 



Fig. 9. Dorsal Views of Skulls 

 Cyrtodelphis sulcatus, Lower Miocene, Italy. Argyrocetus patagonicus, Lower Miocene, Patagonia. Eurhino- 

 delphis bossi, Middle Miocene, Maryland. 



one dorsal found in the Patagonian marine 

 formation at Castillo, opposite Trelew, 

 Chubut Territory, formed the basis for 

 Argyrocetus -patagonicus (Lydekker, 1894). 

 This slender-beaked skull shows how 

 widely these early Miocene porpoises 

 have departed from the known Eocene 

 odontocetes, for the postorbital constric- 



length of the premaxillaries as compared 

 with the maxillaries, and has estimated 

 that the former exceed the latter by an 

 interval equivalent to one-fifth of the 

 total length of the skull. The mandible 

 when complete measured about 35 inches 

 in length, of which fully three-fifths 

 was taken up by the symphysis. Some- 



