572 PHOCA VITULINA HARBOR SEAL. 



jaw very much weaker and narrower, and the rami much less 

 bowed outward, scarcely more so than in P. grcenlandica. In 

 this slighter form the teeth are so much smaller that occasion- 

 ally they are placed (in the upper jaw especially) end to end in- 

 stead of being- set obliquely, and even sometimes slightly spaced. 

 Although the skulls are unmarked as to sex, I believe the slighter 

 skulls to be those of females. 



The sexual differences in size and cranial characters in this, 

 the common Seal of our temperate American and European wa- 

 ters, appear to still remain inadequately investigated, and se- 

 ries of sexed examples seem to be still desiderata in our best 

 collections. The only reference to the subject that I recall are 

 the following incidental observations by Mr. John W. Clark, who, 

 in discussing the assumed distinctive characters of Dr. Gray's 

 HaUcyon richardsi, says : " The thickening of the lower jaw may 

 be a sexual distinction. A skull, unquestionably of a male, pos- 

 sesses it in. a marked degree, while that of a female of appar- 

 ently about the same age, is slender." * 



My attention has been forcibly drawn to this matter by a skull 

 (No. 6783, Nat. Mus.) from Plover Bay (Siberian coast of Behr- 

 iug's Straits), which I at first referred unhesitatingly to Phoca 

 ritnlina, when examined in connection with a large series from 

 both the Atlantic, and Pacific coasts of America, but later, when 

 compared again with a smaller series, I thought it might repre- 

 sent a form closely allied to, but still specifically distinct from, 

 P. rltulina probably the so-called Phoca "nummularis". On 

 collating it again with the full series at first examined it seemed 

 undoubtedly to be only an old female of P. ritulina. Aside from 

 the general slighter and more delicate structure of the skull, the 

 most notable differences are the smaller, normally implanted, and 

 even slightly spaced molar teeth, the narrowness of the facial 

 portion of the skull, and the corresponding narrowness of the 

 lower jaw and absence of the abrupt outward curvature of the 

 rami at the last molar. In general form the lower jaw is much 

 like that of P. grcenlandica, except that the vertical width of the 

 ramus is much less, and the plane of its vertical expansion not 

 nearly so oblique. Other skulls, which are undoubtedly those 

 of P. vitulina, so closely resemble this that it is impossible to 

 regard it as otherwise than an exceptionally attenuated female 

 skull of P. vitulina. One or two others in the series, also pre- 

 sumed to be female, have the teeth small and implanted in a 



*Proc. Zoiil. Soc. Loud.. 1873, p. 557. 



