MIOCENE PORPOISES — KELLOGG 143 



anterior margin. Behind the level of the tuberculum the shaft is 

 abruptl}'^ bent downward. 



The length of this rib in a straight line from tuberculum to distal 

 end of shaft is 165 mm.; greatest breadth of shaft at angle, 35 mm.; 

 and greatest breadth of shaft near middle of its length, 26 mm. 



III. IDENTITY OF TRETOSPHYS GABBII (COPE) 



During the year 1868, Prof. E. D. Cope received a miscellaneous 

 collection of vertebrae and other skeletal fragments from a Maryland 

 correspondent, Dr. James T. Thomas. Included among these bones 

 was the caudal vertebra on which Cope based the name Delphinapterus 

 gabbii. Cope did not designate a precise locality. From residents 

 of Charles County information has since been obtained relative to 

 the location of the residence of Dr. Thomas near the Patuxent River. 

 Although it can not now be stated with certainty, in all probability 

 this type vertebra and the other specimens described by Cope were 

 found by slaves who were digging shell marl on the De la Brooke 

 estate. 



No specimens referable to this species were received by the United 

 States National Museum until 1918, when Dr. Rodney B. Harvey 

 excavated the specimen hereinafter described in the cliff south of 

 Chesapeake Beach, Md. 



Genus Tretosphys Cope 



Tretosphys Cope, Proc. Acad. Nat. Sci. Philadelphia, vol. 20, p. 186, 1868. 



Genotype: Delphinaptents gabbii Cope. (Designated by Hay, 

 U. S. Geol. Surv. Bull. 179, p. 591, 1902.) 



Diagnosis: Mandibles strong, with symphysis firmly ankylosed, 

 V-shaped in cross section, attenuated gradually toward anterior end 

 and with anterior half of its length bowed upward; lateral surfaces of 

 symphysis rugose; opposite free hinder portions of mandibles form an 

 acute angle at level where they ankylose as symphysis; 14 teeth 

 located on left mandible anterior to posterior end of symphysis; 2 

 teeth directed forward and upward at extremity of each ramus; 

 roots of other teeth on symphysis implanted obliquely in alveolae, 

 which slope more noticeably backv/ard than inward; alveolae rela- 

 tively large, closely approximated, those in right ramus larger than 

 those in left ramus, and consequently teeth in the two rows were 

 not opposite; teeth single rooted; anterior teeth have relatively 

 smooth enamel on anteroposteriorly flattened crowns that curve 

 inward and backward; teeth from near middle of tooth rows have 

 enamel on outer surface of crown ornamented with fine striae: crowns 



