AUT. 19 



A MIOCENE POBPOISE FROM MARYLAND — KELLOGG 



PRISCODELPHINUS STENUS Cope 



Cope says that he had two lumbar vertebrae of the fossil por- 

 poise Priscodelphinus stenus, but only one (Cat. No. 11240, Academy 

 of Natural Sciences of Philadelphia) was found and this vertebra 

 was figured by Case.^ This is a small vertebra with a very thin an- 

 terior epiphysis, broad neurapophysis, and a thin-edged inferior 

 longitudinal carina; the posterior epiphysis is missing. In general 

 appearance this vertebra resembles the third or fourth lumbars of 

 Stenodelphis. It is characterized by the unusual proportions of the 

 base of the neural spine, the anteroposterior diameter being propor- 

 tionately greater than on the corresponding verlebra of any por- 

 poise of the same size known to the writer. The nearest approach 

 to this type of neural spine is found in the lumbars of Stenodelphvi^ 



3 



Figs. 3-4. — 3, Lateral View (Right Side) of Type Lumbar 

 OF Priscodelphinus stenus Cope. X %. 4, Anterior 

 View of Type Lumbar of Priscodelphinus stenus Cope. 

 X %. (After Case) 



a living porpoise of approximately the same size. When complete 

 the neural spine was several millimeters broader anteroposteriorly 

 at the base, for the thick posterior border has suffered from erosion 

 or breakage. The posterior face of the centrum is flat, with a large 

 central pit and about 14 ridges radiating from it. The anterior 

 epiphysis is depressed centrally. The posterior end of the centrum 

 is lower than the anterior, a modification also present in the lumbars 

 of Kentriodon. Superiorly the sides of the centrum are flat and 

 inferiorly they are concave, a condition which is traceable to the 

 presence of a narrow diagonal groove on each side of the longitudi- 

 nal inferior carina. Each of these diagonal grooves terminates 

 mesially anterior to the middle of the centrum and extends back- 

 ward and upward to the posterior margin of the basal portion of the 

 transverse process. The remnants of the metapophyses indicate that 

 they were more prominent than in Stenodelphis. Although the 

 transverse processes are broken off at the base, they agree with those 



3 Case, E. C, Miocene Atlas, Maryland Geological Survey, Baltimore, pL 13, figs. 

 1«, lb. 1904. 



