%9o'."'] PKOCEEDINOS OF THE NATIONAL MUSEUM. 221 



In filosa and borealis the cardinal teeth in form, position, and angle 

 are very nearly or quite alike. 



In L.jamaicensis, of the same group, the laterals are conspicuous and 

 stroug; the cardinals inconspicuous, the anterior lateral in the right 

 valve prominent and stumpy, the posterior lateral in the same valve 

 elongated, ridge-like. The surface sculpture in Jilosa, borealis, and ja- 

 maicensis differs each from the other; the texture of the shells in these 

 species also varies, the two latter haviug a much firmer and compact 

 aud porcellanous aspect than Jilosa, and Jilosa having a firmer texture 

 than the Santa Barbara form, which latter has a surface aspect in the 

 matter of texture much nearer to L. lamellosa Smith. The latter is a 

 somewhat tumid and angulated form from the Straits of Magellan, aud 

 has a rather rounded tuberculoid lateral on the anterior side of the 

 valves. 



The anterior dorsal region, it will be seen by looking at the figures, is 

 markedly different in Stimpson's ,/i/as« from wquizonata. 



Suborder Veneracea. 

 Family Venerid^e. 



Genua VENUS Liun. 



Subf^euus CiiiONE Megerle. 



Venus (Chione) effeminata sp. no v. 



Plate XVII, Figs. 1,2. 



Shell triangularly transversely ovate, the anterior outline rounded, 

 the posterior more elongated and obtusely angulate. The proportions 

 of the shell are as follows: Three-fifths of the length are posterior to a 

 (perpendicular) line drawn from the umbones to the ventral margin ; the 

 height of the shell on said line as compared with the length is as four 

 to five. 



The valves are moderately convex, and the surface is prettily and 

 evenly cancellated by forty-five to fifty rounded ribs radiating from the 

 beaks and divided by grooves of nearly the same width as the ribs ; both 

 ribs and grooves are crossed by thirty to thirty-five or more sharp, 

 elevated, concentric, thread-like strite, so fine at the beaks as to be 

 scarcely discernible. Color whitish, purplish in the umbonal region. 

 The beaks are pink, sharp, proximate, and turned towards the lunule, 

 which latter is ov^ately cuneiform and distinctly defined. The ligamental 

 area is narrow, elongated, somewhat excavated, and slightly keeled. 

 Interior of valves rosy purple aud crenulated on the edges from a point 

 about midway up the anterior margin to a similar i^oint on the opposite 

 end, the crenulations peculiarly sharp and squarely cut. 



Hinge j^late moderately thick ; the right valve exhibits two strong 

 aud one upper thin elongated subsidiary tootli, just under and parallel 



