MIOCENE PORPOISES — KELLOGG 151 



The neural canal is narrow and rather high. The dorsal surface 

 iof the centrum is depressed medially, and also laterally on each side 

 of the median thin longitudinal carina. 



The type is an anterior caudal vertebra, probably the second or 



third, that lacks the neural spine and the transverse processes exxept 



for their basal portions. The anteroposterior diameter of the centrum 



1(52.6 mm.) is greater than its transverse width anteriorly (40.7 mm.). 



I The vertical diameter of the anterior face of the centrum is 37.4 mm. 



i Viewed from the side the lateral surface of the centrum is seen to be 



; depressed between the base of the transverse process and the base of 



(the pedicle of the neural arch, and the ventral profile is markedly 



i concave. On the ventral surface of the centrum two parallel ridges 



! bound a longitudinal groove approximately 8 mm. in width. Each 



Iof these ridges is widened posteriorly for articulation with the cor- 



: responding chevron bone. A shallow groove extends backward from 



• near the anterior epiphysis above the base of the transverse process 



but becomes indistinct posterior to the middle of the latter. The 



basal portions of the transverse processes furnish some indication of 



their conformation. At the base, the right transverse process is 



; approximately 28 mm. wide. When complete, these transverse 



I processes may have resembled those of the corresponding vertebrae 



i of Delphinodon dividum. The neural canal was narrow and rather 



low, about 8 mm. in height. The pedicles of the neural arch are flat 



externally, and at the base occupy less than half the length of the 



centrum. The epiphyses are relatively thin, firmly ankylosed to the 



centrum, and concave centrally. 



A posterior dorsal vertebra (pi. 19, fig. 3), presumably the ninth 



in the series, that agrees with Tretosphys gabbii in size and general 



characteristics was found by Norman Boss during August 1913 in 



Zone 11 four feet above the shell band (Zone 10), Iji miles south of 



' Chesapeake Beach, Calvert County, Md. This vertebra lacks both 



' epiphyses, and the transverse processes and the metapophyses are 



incomplete. 

 I The posterior surface of the centrum is approximately the same 

 width as the anterior surface, the metapophyses are rather short and 

 slender, and the prezygapophysial facets are reduced in size. The 

 neural spine is rather broad near base (35 mm.), and commencing 

 ' about 25 mm. above the level of the metapophyses tapers rapidly to 

 extremity. The pedicles of the neural arch are rather broad, and 

 are not noticeably inclined forward. The centrum is longer than 

 broad. Below the transverse process the lateral surface of the centrum 

 is concave from end to end and the ventral surface is pinched-in to 

 form an anteroposterior ridge. The dorsal surface of the centrum 

 is depressed medially, and also laterally on each side of the median 



