164 BULLETIN OF THE 



flat, not rising above the body whorl ; suture well impressed ; umbilicus moderately 

 large, exhibiting most of tlie volutions ; aperture transversely subcircular, wider 

 than liigli ; lip simple, thickened, sinuous above, very slightly reflected at the base, 

 ends scarcely approaclied. Width f'^ inch, height ^^ inch. 



Hills near Oakland, California. One specimen only. 



Tliis rare and interesting little shell I collected some years ago. It is a perfect 

 miniature form, in every respect, of aS'. Vancouverensis. I regard it as an extremely 

 small variety of that so called species. It is about the size of the variety of 

 aS. Duranti, lately described as S. cceiatus, 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, Hemphul. 



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 f mch, 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 Vancouveirensis. 



All our American Selenites commence life with a finely granulated shell. When 

 they have attained about two whorls, the striae 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 tlie laws of their constitutional characteristics and the environment, among 

 which I include afiinity of matter and mechanical skill, the latter a faculty pos- 

 sessed to a greater or less degree by all animals. Some individuals m a colony of 

 shells display greater meclianical 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- 

 bilicus generally follows the change m 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 



