ABT. 19 A MIOCENE PORPOISE FROM MARYLAND KELLOGG 23 



Aside from its smaller size, the left periotic (pi. 3, figs. S-4) differs 

 from that of Delphinodon dividum in that the pars cochlearis is less 

 expanded horizontally, the tractus spiralis foramiriosus is longer and 

 the curvature of the spiral is less pronounced, the fossa incudis is 

 narrower, the elongate foramen singulare is placed on the rim of the 

 low partition between the spiral tract and the entrance to the Aquae- 

 ductus Fallopii, and there is a well-defined concavity on the ventral 

 surface of the pars cochlearis at the anteroexternal angle. No peri- 

 otics of the living southern porpoise Sotalia were available for com- 

 parison. Van Beneden figured two views of the right periotic of 

 Sotaliu, guianensis. Judging from the illustrations used by Van 

 Beneden " the periotic of Sotalia resembles this fossil periotic rather 

 closely; the configuration of the cerebral surface and the shape of 

 the internal acoustic meatus are similar, but they differ from one 

 another in the positions of the entrance to the Aquaeductus Fallopii 

 and the cerebral orifice of the Aquaeductus cochleae. Although this 

 periotic is approximately the same size as that of the living porpoise 

 Prodelphinus malayanus (Cat. No. 36051, U.S.N.M.), it differs from 

 the latter in several respects, of which the shape of the internal 

 acoustic meatus and the articular facet on the posterior process are 

 probably the most obvious differences. 



One characteristic feature of the ventral surface of this periotic 

 (fig. 6) is the shape of the articular facet on the posterior process. 

 This articular facet is deeply concave on the basal portion and the 

 surface slopes from the apex to the internal margin. A few faint 

 shallow grooves may be distinguished on the outer border of this 

 facet, but they gradually disappear as they approach the above-men- 

 tioned concavity. The ventrointernal border of the posterior process 

 projects inward and the free edge contributes the floor for the facial 

 canal. The anterior face of the posterior process is excavated; the 

 external face is somewhat flattened ; and the posterior face is rather 

 evenly convex. 



As regards the ventral aspect of the pofrs cochleaHs^ there is a 

 much closer resemblance to Prodelphinus malayomwis than to Del- 

 phinodon dividum. The continuation of the facet for the accessory 

 ossicle or uncinate process of the tympanic, usually limited to the 

 anterior process, over upon the ventral surface of the pars cochlearis 

 is an unusual modification. Nothing quite like this has been noticed 

 on the periotics of living porpoises. The pars cochlearis of this 

 fossil periotic also differs from those of both Prodelphinus mcdayarms 



" Van Beneden, P. J., and P. Gervais, Osteographie des Cetac6s vlvaols et fossiles, 

 Paris, Atlas, pi. 41, figs. 8, 8ff, 1880. 



