LACUNA. 



303 



angle. A slight angular ridge revolves from the upper angle of the 

 aperture, on some specimens quite perceptible. Operculum horny, 

 sub-spiral. Length, one half inch ; breadth, three tenths of an 

 inch; divergence, fifty-eight degrees. 



Yar. fusca. Fig. 178*. Shell proportionally shorter, more solid 

 and opaque, of a darker, generally uniform color, sometimes yellow- 

 ish, and sometimes purplish horn color, occasionally with one or 

 two bands, or banded shades; the mouth more angular, and the 

 angular revolving ridge more frequently conspicuous. 



Found, driven up, on all our beaches, and alive among the roots 

 of Laminaria and other marine plants, attached to stones and shells, 

 and dragged by storms from deep water. Eastport ( Cooper) ; Fish- 

 ing Banks (Willis) ; whole coast of New England (Stimpson). 



It is easily distinguished from all our shells by its peculiar umbil- 

 icus, and its elongated form, by which it is distinguished from the 

 next species. The size above given is larger than in most speci- 

 mens, but not so large as in many. It is undoubtedly the L. vincta 

 of the British shores, as settled by actual comparison and the opin- 

 ion of Mr. Sowcrby. Mr. Conrad seems not to have been acquainted 

 with the L. vincta, when he described his L. pertusa, distinguishing 

 it from L. quadrifasciata. The variety is found in about equal 

 numbers with the type. It does not depend on age; for small 

 young specimens are proportionally short, dark, and solid. But 

 the approaches to each other are so insensible, that I do not ven- 

 ture to make a species of it ; but attach to it, as a variety, a name 

 some years since proposed for it by Dr. Binney. It may prove to 

 be a technical species, and perhaps is actually the Turbo canalis, 

 Montagu. 



Lacuna neritoidea. 



Fig. 170. 



Shell globular-ovate, with three whorls and a half, the last very large, smooth, 

 yellowish-green ; aperture semi-lunar, oblique ; umbilicus large and deep. 



Lacuna neritoidea, Gould, Sillim. Journ. xxxviii. 197; Inv. 1st cd. -263, lig. 170. — 

 Stimpson, Check Lists, 5. 



Shell small, thin, hemispherical, or obliquely-ovate ; whorls three 

 and a half, regularly convex, minutely wrinkled near the suture, and 

 with an occasional transverse scratch ; otherwise smooth, and cov- 

 ered with a rough, greenish-yellow epidermis ; the sutural region is 

 depressed and sub-channelled ; the spire is scarcely prominent above 

 the very large lower whorl, and is placed a little to one side ; aper- 



