4 PROCEEDINGS OF THE NATIONAL, MUSEUM. vol. 6S, 



plete, the canal narrow and slitlike posteriorly and broadly oval 

 anteriorly. This vertebra is peculiar in- having the transverse proc- 

 esses set in elliptical depressions, divided posteriorly by a thin ridge 

 extending back from the base of the process. This depression is 

 bounded superiorly by a longitudinal ridge, above which is another 

 depression at the base of the neural arch. The posterior epiphysis 

 is thick and flat. The articular surface has about 12 or 14 radiating 

 lines. The double keels ^ are emarginate at the middle, and the 

 surface of the centrum between them concave. This caudal belonged 

 to a large porpoise as is shown by the following measurements. 



mm. 



Length of vertebra (one epiphysis lacking)-. 101 



Greatest depth of centrum 59 



Breadth of centrum anteriorly (worn) 55 



Depth of centrum anteriorly (worn) 53 



Height neural canal antex'iorly 12 



Height neural canal posteriorly 27 



Length of base of neural arch (where margins are vertical) 41 



Length of base of transverse process (about) 25 



Height of depres.«>ion surrounding transverse process (measured to eniargi- 



nation of keel below) . 42 



A satisfactory comparison of the present specimen and the vertebra 

 upon which Cope based Zarhachis flagellator^ however, is not possible 

 as the corresponding vertebra was not found. The measurements for 

 the lumbar vertebrae of the specimen from the Calvert Cliffs and 

 for the caudal of Zarhachis fiageXlatoT bear out the assumption that 

 they belong to the same type of cetacean. In addition to a corre- 

 spondence in size of the vertebrae, there are certain structural pe- 

 culiarities which favor such an association. The posterior lumbars 

 of the fossil porpoise from the Calvert Cliffs have an elongate 

 centrum as well as a relative narrow and deep neural canal. The 

 neural arch does not occupy the full length of the centrum and on 

 the largest caudal there are double ventral keels and corresponding 

 development of the depressions on either side. There is no trace, 

 however, of a longitudinal keel above the transverse process. The 

 type caudal of Zarhachis flagellator^ as remarked above, is peculiar 

 in having the transverse processes set in elliptical depressions, but 

 on the whole the structural features of this caudal vertebra and those 

 of the lumbars described in the following text are of the same general 

 type, when one takes into consideration the corresponding differ- 

 ences between the lumbar and caudal vertebrae of the living por- 

 poises, Platanista gangetica and Inia geoffrensis. In addition both 

 of these specimens were obtained from deposits belonging to the Cal- 

 vert formation. 



•Case,. E. C, Miocene Atlas, Maryland Geol. Surv., Baltimore, pi. 14, fig. 3, 1904. 



