24 ACM^A. 



It is worthy of note that when there is a brown marking on the 

 exterior, in the region of the sub-marginal internal mottled band, 

 the latter is interrupted by a white space corresponding in size and 

 width to the external marking. (Da//.) 



A. (Collisella) peramabilis DALL, Proc. Cal. Acad. Sci. iv, p. 302, 

 Dec. 17, 1872 ; Proc. U. S. Nat. Mus. i. p. 341, 1878. 



My figures are drawn from a type specimen. It is a most 

 beautiful shell, as delicate in coloring as a rose-petal. 



A. APICINA Dall. PL 7, figs. 66, 67. 



Shell small, conical, thin, rounded, more or less elevated ; whitish 

 or isabelline, the apex erect, buff; inside buff, whitish or brown, 

 smooth ; provided with subobsolete lines of growth outside. Length 

 6, breadth 5, alt. 4 mill. (Dall.) 



Pribiloff Is. on the north ; Aleutians from Amchitka eastward to 

 the Shumaging, 0-70 fms. 



A. ( ColUsella /) apicina DALL, Proc. U. S. Nat. Mus. i, p. 341, 1878. 



Among other small shells obtained from time to time on the beach 

 or in the dredge, occasional specimens occurred which at first were 

 supposed to be the young of A. mitra or pale specimens of A. sybar- 

 itica. After eliminating some of the these, there remained, after care- 

 ful study, a residue which 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 polished. Within, fresh specimens are 

 yellowish, whitish or orange-colored, and quite polished. The out- 

 side is almost always covered with Nullipore. The chief characters 

 are the rounded base, regularly conical and yellow spotted apex, 

 with a thinner shell than A. mitra. (Dall.) 



My figures are drawn from one of the types in the Smithsonian 

 Institution, no. 30787 of the museum register. It is allied to 

 A. mitra and A. virginea. 



A. MITRA Eschscholtz. PI. 3, fig. 50. 



Shell dull- white, aperture nearly circular, wider behind, in some 

 young examples somewhat elongated, oval; form conical, apex erect, 

 nearly central, blunt, smooth, posterior surface usually straight, but 

 occasionally a little convex ; exterior smooth, marked with very 

 faint concentric lines of growth, devoid of epidermis ; margin entire, 

 polished, with a narrow semi-pellucid rim inside. 



