164 BULLETIN OF THE 
flat, not rising above the body whorl; suture well impressed; umbilicus moderately 
large, exhibiting most of the volutions; aperture transversely subcircular, wider 
than high; lip simple, thickened, sinuous above, very slightly reflected at the base, 
ends scarcely approached Width % inch, height 5 inch. 
Hills near Oakland, California. One specimen only. 
This rare and interesting little shell I collected some years ago. It is a perfect 
miniature form, in every respect, of S. Vancouwverensis, I regard it as an extremely 
small variety of that so called species. It is about the size of the variety of 
S. Durant, lately described as S. cwlatus, Mazyck, but differs very materially in form, 
sculptnre, and the general texture of the shell. It differs from var. Catalinensis in 
being more robust, larger, and has a smaller umbilicus. I dedicate this pretty little 
shell to Prof. Josiah Keep, of Mills College, California, who has done so much 
through his interesting little book to stimulate the study of West Coast shells. 
The above is Mr. Hemphill’s description, from “The Nautilus,” Vol. IV. 
p. 42, 1890. My figure is drawn from an authentic specimen, 
Selenites Vancouverensis, var. hybridus, Humeutte. 
Shell broadly umbilicated, depressed, slightly convex above, surface shining, 
polished, of a dark yellowish green color, lines of growth coarse, rib-like and regu- 
lar on the spire, finer and more irregular on the body whorl, crossed by fine revolv- 
ing lines that become fainter on the last whorl, suture well impressed; aperture 
rounded, broader than high, greatly indented above; lip simple, very little reflected 
below at its junction with the columella, very sinuous above, its terminations joined 
by a very thin callus. Height § inch, breadth 1 inch. 
Astoria, Oregon. 
In the strong rib-like sculpturing of the spire, depressed form, and sinuous lip, it 
resembles sportellus. In its greater diameter, dark greenish color, and the absence 
of the decussating sculpture on the last whorl, it approaches Vancouverensis. 
All our American Selenites commence life with a finely granulated shell. When 
they have attained about two whorls, the stria begin to appear, and increase in 
strength as the shell increases in size. 
It is well known that all shell-bearing mollusks construct their shells in obedi- 
ence to the laws of their constitutional characteristics and the environment, among 
which I include affinity of matter and mechanical skill, the latter a faculty pos- 
sessed to a greater or less degree by all animals. Some individuals in a colony of 
shells display greater mechanical skill than others, or possess stronger imitative 
powers, and closely follow the lines and styles of their forefathers, strictly attend- 
ing to the details of sculpturing, not omitting a rib or line, Other individuals of 
the same colony, not having this imitative faculty so strongly developed, may 
change or vary the form of the shell by constructing it with more convex whorls, 
generally resulting in a narrower or more elevated shell; or they may flatten the 
whorls, resulting in a broader and depressed form. Some modification of the um- 
bilieus generally follows the change in the form of the shell. In both cases the 
sculpturing may be what we call characteristic of the species, or may be more or 
less modified by the omission of one, two, or more ribs, or the ribs may be more 
