OF CONCHOLOGY. 133 



ward the margin. These are crossed by evident but not very 

 strong lines of growth, which, in some individuals, are rather 

 strong. Anterior declivity of the shell concave, sides flattened, 

 posterior declivity rounded convex. Color whitish, with numer- 

 ous radiating rays of brown or slate color, usually with a broad 

 fasciculus of darker rays in the middle of each side extending 

 from the apex to the margin, and occasional dark dots on the 

 ribs. Shell occasionally entirely brown or slate color, with two 

 darker rays on the sides. Epidermis none. 



Interior pure white, the two dark rays sometimes showing 

 through the shell. Extreme outer edge finely denticulate or 

 rounded and smooth according to the stage of growth. Margin 

 as a whole broad, smooth, differentiated from the rest of the sur- 

 face by a wide, shallow groove. Margin of the aperture simi- 

 larly bordered. Muscular impressions distinct, surface marked 

 by fine radiating lines ; polished. Anterior and posterior mar- 

 gins internally concave or emarginated, so that when laid upon 

 a flat surface in the natural position the ends of the shell do not 

 touch it. 



Adult, Ion. '1 ; lat. *5 ; alt. "2 in. Lon. of aperture, *23 ; lat. 

 of do., 12 in. 



Habitat. — Monterey, California, dead on beach, ten specimens, 

 Dall, 1866. Alive under stones at low water, Stearns, Cooper. 

 Also at Baulinas Bay, Santa Barbara, Purissima and Lobitas, 

 Cala., Stearns and Newcomb. 



The dark lateral bands and markings are not invariable, though 

 pretty constant, and had not the shell in question been published 

 in several catalogues and become familiar to Californian con- 

 chologists for five years, under my MSS. name, I should have 

 preferred to substitute another. 



The nearest ally of this species is the Clypidella callomargi- 

 nata, of Dr. Carpenter. 



The hitherto unique type being in the Smithsonian Collection 

 I have not failed to compare it carefully with a good series of 

 the present species, and feel no doubt as to its specific and per- 

 haps generic distinctness. In the callomarginata the relations 

 of the margin are exactly reversed ; the sides are slightly con- 

 cave, and the ends are convex and produced. The aperture is 

 much smaller and narrower than in a specimen of bimaculata 

 half the size ; the sculpture, though on the same plan, is sharp 

 and rough, the lines of increase being prolonged into sharp, 

 elevated scales, and the ribs nodulous ; while the exterior is 

 covered with a rather coarse epidermis and adherent annelid 

 tubes, showing conclusively that it could not have been, like the 

 present species, an internal or partially internal shell. The 



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