ART. 14. MARYLAND FOSSIL PORPOISE KELLOGG. 7 



Chesapeake Beach, Calvert County, Maryland. Shown on Patuxent 

 quadrangle or Patuxent folio. No. 152, United States Geological 

 Survey. 



Horizon. — The specimen was discovered and excavated by Nor- 

 man H. Boss on August 8, 1921. It was dug from the cliffs three 

 feet (0.92 meter) above the water level. The oyster shell zone is not 

 visible at this point, and lies below the beach level. The specimen 

 was dug from Shattuck's zone 5 of the Calvert Miocene formation 

 of Maryland. 



It may seem surprising that the skull of this fossil porpoise 

 manifests many of the peculiar features of Platanista, Lipotes., and 

 Inia. The combination of characters is of much interest, though 

 this form can not be considered an ancestor of any of these living 

 genera. Although the skull of this fossil porpoise possesses more 

 features in common with Lipotes than with Inia^ there are obvious 

 differences in the details of structural modification which are present 

 throughout those parts of the skeleton which are available for com- 

 parison. 



The resemblance of certain portions of the skulls of Lipotes and 

 Platanista to this fossil is undoubtedly a common inheritance from 

 more primitive ancestors. The modifications of the bones which take 

 part in the formation of the nasal passages and the structural 

 peculiarities of the premaxillae are essentially the same in all three 

 skulls. This fossil skull in common with Platanista possesses a 

 large expanded external pterygoid, a deep groove between the 

 squamosal and frontal bones, a zygoma with broad glenoid surface, 

 a supraorbital process in contact with the zj^goma, maxillary teeth 

 with narrow recurved crowns, and a peculiar type of tympanic and 

 periotic bones. 



Skulls of Lipotes and Inia may appear more specialized than that 

 of Zarhachis because of the elevation of the vertex and the shifting 

 of the nasals to a vertical position. On the other hand, the skull 

 of Zarhachis is characterized by an unusually long attenuated ros- 

 trum, by the great vertical depth of the extremity of the supraorbital 

 process, and by a zygomatic process which extends forward beyond 

 the level of the anterior wall of the brain case and underlies the 

 postorbital projection of the frontal. Lipotes possesses a rather 

 high maxillary crest, but the extremity of the supraorbital process 

 is relatively shallow and the rostrum is proportionately shorter than 

 in Zarhachis; the frontal plate of the maxilla is nearly horizontal 

 above the temporal fossa and the rostrum is constricted behind the 

 tooth rows. In Inia., however, the outer edge of the frontal plate of 

 the maxilla is bent upward and forms a vertical crest above the tem- 

 poral fossa, the extremity of the supraorbital process is less strongly 

 curved upward, the premaxilla in front of the nasal aperture is 



