6 PROCEEDINGS OF THE NATIONAL MUSEUM vol.6, 



Horizon. — This skull was discovered and excavated by William 

 Palmer during^ July, 1918. It was dug from the face of the cliff 

 about 3 feet below the level of the oyster shells {Ostrea perorassa) 

 in the bluish sandy clay of the upper part of Shattuck's zone 3 of 

 the Calvert Miocene formation of Maryland. 



Most of the characteristic porpoises which frequented the seas 

 along the Atlantic Coast of North America during Miocene times 

 disappeared from these waters near the close of that period, for they 

 are not known from subsequent formations, and other species which 

 were developing elsewhere took their places in the pelagic faunas of 

 succeeding geological periods. We have no evidence that the fossil 

 porpoise here described is ancestral to living propoises, like Lisso- 

 delphis^ Delphinus, Steno^ and Prodelphinus., but there is a marked 

 resemblance between this fossil species and the living SotaXia. This 

 fossil propoise undoubtedly belongs in the family Delphinidae, 

 although it should not be placed in the same section with Delphinus 

 and Steno, but rather with Sotolia. It does not represent, however, 

 tin intermediate stage between Sotalia and any other known fossil 

 porpoise. The skeleton of this porpoise was approximately 5^/2 feet 

 long. 



The graceful undulating movements of some of the smaller Del- 

 phinidae are familiar to all who have observed a shoal of these ani- 

 mals in pursuit of a school of fish. The individuals in a shoal of 

 porpoises often swim in a line one before another, never showing 

 at the surface more than the dorsal fin and a small portion of their 

 backs. At times they spring from the vvater and leap a considerable 

 distance. The skeletons of the Miocene porpoises, Delphinodon 

 dividimi and Kentiiodon pernix., resemble those of some of the 

 smaller living porpoises very closely, and it is not unlikely that they 

 were as active and as graceful as any of the living types. Judging 

 by the skeletons of the fossil porpoises which are more or less fully 

 known, there has been a tendency toward greater progressive changes 

 in the structural modifications of some types than in others. In 

 general these modifications have facilitated feeding and swimming. 

 Less progressive, less active, and less plastic species of several types, 

 particularly Sqnalodon^ frequented the Miocene Chesapeake estuary 

 at the same time as Delphinodon dividum and Kentriodoiy pei^nix. 

 More highly modified and possibly more active species, like Zarliachis 

 -fiagellator, E urhinodelphis hossi, and Schizodelphis crassanguluTH 

 also entered the same estuary. 



Fish-eating porpoises predominate among the living Delphinidae, 

 but there are some that feed largely on cuttlefish, squids, and crus- 

 taceans. That these Miocene porpoises differed from one another in 

 their feeding habits is suggested by the modifications observed in the 



