342 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



After eliminating- some of tliese, there remained, after careful study, a 

 lesidue, wliicli do not appear to coincide in character with any described 

 species. They are small, thin, conical, with a blunt, erect apex marked 

 by a light yellow spot, the rest of the exterior white or faintly yellowish, 

 marked by obsolete lines of growth, smooth, or nearly so, but not pol- 

 ished. AYithin, fresh specimens are yellowish, whitish, or orange-col- 

 ored, and quite i^olished. The outside is almost always covered with 

 nullipore. The chief characters are the rounded base, regularly conical 

 and yellow spotted apex, with a thinner shell than young A. mitra. 



Fam. PATELLID.E. 

 Genus i^ACELLA Schumacher. 



Nacella (Schum.) Dall, 1. c. p. '274, 1871. Type X mytilina Gm. 



Nacella? rosea. 



Nacella? rosea Dull, Proc. Cal. Acad. Sci. iv, p. 270, pi. 1, f. 2, Oct. 1872. 



Hah. — Dead on exi^osed ocean beaches at Kyska Island, Aleutians, 

 and Sijneonoff Island, Shumagins. Alive onfuci off shore? Forty-five 

 spe(;imens obtained, all dead. 



This exquisite little rose-leaf of a shell exactly resembles the type of 

 the genus Nacella in form, and is the only one of the so-called Nacellw of 

 ihe northwest coast which has not been proved to be an Acmceid. It 

 is only provisionally referred to this family, and may prove, like the 

 others, non-i)atelloid when the animal becomes known. 



In tliis connection it may be of interest to quote the words of Esch- 

 scholtz in describing th^ genus Acma'a,* words Avhich at one time were 

 partially discredited, but which the march of science has proved literally 

 true: — "Here" (at Sitka) are found "six species of a genus which from 

 its simple unwound shell would be immediately taken for a Patella ; the 

 creature, however, closely resembles the Fissurella, with the difference 

 that only one gill is visible in the fissure over the neck. It is remark- 

 able that on the whole northwest coast of America, down to California, 

 no Patella, only annuals of the genus Acmwa were to be met with." 



It Avill be noticed from the preceding' documents that in the Alaskan 

 region fourteen si^ecies of Limpets, not counting the innumerable varie- 

 ties, and twenty-six or seven species of CMtonidw, are known, most of 

 which have rewarded our researches, and a part of which are absolutely 

 new. Additional species may be expected to recompense additional 

 and more minute research ; but that the chief members of these groupw 

 uati^'e to this region have been determined there is little reason to doubt. 



* From the Englisli rei)rint, piiblislied in the spriug of 1830, but dated by the author 

 at " Dorpat, Jau. 7, 1828." I found the first edition in the Eoyal Library at Stock- 

 holm. It i)assed the censor in March, 1829, was issued in the winter of 1829-30, and 

 is dated on the titlepago 1830. 



