324 Mr. A. Hancock on Shells dredged on 



undatum, about which a few remarks may be desirable. The 

 allies of this species appear to be little known, and it is, therefore, 

 with some hesitation that I have ventured to describe what I con- 

 ceive to be three or four new species of them : this I should 

 scarcely have done, had they been from different localities and 

 from various depths of water. 



The three principal varieties of B. undatum are never found 

 mingled together ; so far as I know, they belong to distinct loca- 

 lities ; and their difference of appearance is probably owing to 

 this cause. The variety with a coloured mouth, flattish whorls, 

 and short conical spire is always procured between tide-marks ; 

 the heavy, coarse and much -waved shell, without an epidermis, 

 belongs to a hard gravelly bottom, in about twenty fathoms water ; 

 and the variety with a thin delicate shell and soft velvety epi- 

 dermis is procured at the depth of forty fathoms or more, on a 

 soft bottom. The new species here described are all, however, 

 from the same locality, and from the same depth of water. The 

 peculiarities, then, of these species can scarcely be the effect of 

 external circumstances, and it would therefore seem probable 

 that they are specifically distinct ; but whether so or not, it is 

 proper that forms apparently so permanent and so strongly 

 marked should be known ; and with this view I have sunk other 

 considerations, feeling assured that a knowledge of varieties is 

 essential to a correct discrimination of species. 



Littorina tenebrosa, Montagu sp. 



Turbo tenebrosus, Mont. Brit. Shells, p. 303. 



A few specimens of. a Littorina closely resembling this species 

 were gathered on the rocks surrounding the bay where the col- 

 lection was made; they are chiefly of a dark hue, tessellated 

 with yellowish brown, and with the whorls much rounded. 



Margarita umbilicalis, Brod. and Sowerby. 

 Margarita umbilicalis, Brod. and Sow., Zool. Journ. vol. iv. 

 p. 371. 



This fine species occurred in great abundance and of a large 

 size, some measuring upwards of an inch in diameter. 



They vary from a pale yellowish horn-colour to a dark purplish 

 flesh-tint, and some have the spiral striae nearly obsolete : these 

 are always strongest on the spire. Several of the shells are 

 covered with an exceedingly thin, glossy, horn-like, transparent 

 epidermis ; operculum horny. 



Margarita sordida, mihi. 

 Margarita striata, Brod. and Sow., Zool. Journ. vol. iv. p. 371 ; 

 Sowerby, Zool. Beechey's Voy. p. 143. pi. 37. fig. 11. 



Not by any means so abundant as the former species. Oper- 



