124 BULLETIN 3a, UNITED 8TATES NATIONAL MUSEUSI. 



type-skull, wlieii compared with a skull of i'. commnnis, present a iiuui- 

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

 The skulls of P. DaUil are remarkable for their short, flat beaks and 

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

 of the nares than in P. communis, and nearly flat sujieriorly. 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 deep, 

 narrow grooves as they do in P. cormmmis. Tbe intermaxillaj are sepa- 

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

 trough the vomer is j^lainlj' visible. The region of the skull between 

 the nares and the occipital crest is nearly at right angles with the i)lane 

 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 fossa'- are small, and 

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

 terior, are very large. 



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

 are discernible — together with the dilferences 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 

 ray i^revious paper on this species : 



Alcasurcmcnts of ihc exterior of a specimen of rhocw>ia daUil eapiured off Adalli Islaud, 



August -[3, 1S73. 



[These measurements are iu straight lines, the curves of the bjdy being excluded.! 



Inches. 



Total length 72.0 



Tip of lower jaw to corner of mouth 3. 5 



Tip of lower jaw to center of eye T. 



Tip of lower jaw to ear I). "> 



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



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



Tip of lower jaw to anterior edge of blowhole D. 



Eye to spouthole (vertical) 4.0 



Across base of pectoral !j. T) 



Anterior base of pectoral to lip 8. 



Posterior base of pectoral to tip 5. 75 



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



Spouthole to anterior edge of dorsal 18.5 



Height of dorsal «. 



Length of base of dorsal 10- •'> 



Length posterior margin of dorsal 7.5 



Tip of lower jaw to genital slit 4:5. 



Leugth of genital slit 3. 



Genital slit to anus 4.25 



Anus to notch of the Unices 22. 75 



I?readth of flukes (transverse) 18.5 



Length of flukes (antero-posterior) 5. 25 



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



