124 BULLETIN 30, UNITED STATES NATIONAL MUSEUM. 



type-skull, wlien compared with a skull of J\ communis, i^iesent a uuin- 

 ber of characters by which the two species are readily distiuguishable. 

 The skulls of F. DaUii are remarkable for their short, tiat beaks aud 

 great breadth between the orbits. The iuterranxilhe are higher in front 

 of the nares than in P. communis, and nearly flat superiorly. The tri- 

 angular area in front of the nares is raised above the level of the sur- 

 rounding surface and the foramina on either side do not open into deeji, 

 narrow grooves as they do in P. communis. The intermaxillfe are sejia- 

 rated at their inner margins by a wide space, and at the bottom of the 

 trough the vomer is plainly visible. The region of the skull between 

 the nares and the occipital crest is nearly at right angles with the plane 

 of the beak. The nasal bones have the form of two transverse, promi- 

 nent bosses. The occipital bone is exceedingly large and broad, as com- 

 pared with that of P. communis ; the temporal foss;e are small, and 

 the squamosal are short and thick. The nares, both superior and in- 

 ferior, are very large. 



These difi'erences in the skull — and they are but a few of those which 

 are discernible — together with the differences in external appearance, 

 separate this species very clearly from P. communis, and there can be 

 no doubt that it is distinct and valid. 



I repeat in this connection the measurements of the exterior given in 

 my previous paper on this species : 



Measurements of the exterior of a specimen of riioavna dalUl captured ojf Adalcli Island, 



August 13, 1873. 



[These measurements are in straight lines, the curves of the hjdy being excluded. 1 



Inches. 



Total length - 72.0 



Tip of lower jaw to corner of mouth 3.5 



Tip of lower jaw to center of eye 7. 



Tip of lower jaw to ear D. 5 



Tip of lower jaw to front edge of pectoral at its insertion 11. 



Tip of lower jaw to back edge of jiectoral at its insertion 14. 



Tip of lower jaw to anterior edge of blowhole *J. 



Eye to spoutbole (vertical) 4. 



Across base of pectoral 5. 5 



Anterior base of pectoral to lip 8. 



Posterior base of pectoral to tij) 5. 75 



Tip of lower jaw to anterior boundary of the white area 27. 3 



Spoiitholo to anterior edge of dorsal 18.5 



Height of dorsal C. 



Length of base of dorsal 10.5 



Length posterior margin of dorsal 7. o 



Tip of lower jaw to genital slit 43. 



Length of genital slit 3. 



Genital slit to anus 4. 25 



Anns to notch of the flukes 22. 75 



Breadth of flukes (transverse) 18. 5 



Length of flukes (antero-postcrior) 5. 25 



Breadth of narrowest part of tail before the flukes 1. 75 



