MARSHALL: ADDITIONS TO " I5RITISH CONCHOLOGY." 131 



some study, with a liberal supply of specimens. Only an intimate 

 acquaintance with its many forms, which few collectors have the 

 patience to go through, can give an idea of their variability. 



The ribbed shell is the prevalent form at Bantry, where it lives in 

 sea-weeds at low water, and may also be dredged just outside Glen- 

 gariff Harbour, but from other localities the smooth shells prevail. 

 There are two sizes almost everywhere, but at Connemara they are all 

 dwarfs, showing that this cannot be the male, as surmised by Jeffreys. 

 The bulk of these latter are smooth, and might easily be taken for 

 R. inconspicua var. variegaia, but the whorls are not flattened nor the 

 base angulated as in that variety. Most of the specimens from 

 Torbay are narrower than the type, running even to an oblong shape, 

 and these differ from var. sarsi in being more solid and having a 

 labial rib. At Barra, in the Outer Hebrides, R. albella is very abun- 

 dant and varied in form. 



No British specimens are as tumid as those from the Baltic, which 

 are the most perfect and typical of the species. Specimens may be 

 found of every degree of length and breadth, every degree of sculp- 

 ture, size, convexity, suture, and markings. The colouring is usually 

 obscure both in the type and variety, but when visible on the smooth 

 shells the markings appear as short reddish-brown streaks, straight on 

 the upper whorls and fiexuous on the last two, though in some rare 

 cases they have broad and continuous longitudinal streaks throughout. 

 A dwarf from Torbay is of the same size and resembles R. incon- 

 spicua var. variegala, but the former has convex whorls and an 

 umbilical chink, otherwise I have never seen a connecting link 

 between the two species, though R. albella approximates to R. parva 

 in several forms. A broad and tumid form of R. parva var. inter- 

 rupta is marked off from the smooth shells of this by the thick 

 bevelled aperture and coloured streak outside, and the same cha- 

 racters separate the var. semicostata from half-ribbed R. albella. A 

 narrow form with compressed whorls and shallow suture, from Jersey, 

 is shaped as R. parva var. interrupta, but the markings are different. 



I have dwelt thus largely on this particular species because I 

 know of no other member of the genus that gives such trouble to 

 collectors. 



The var. sarsi is usually narrower than the type, as in Jeffreys' 

 figure, and is occasionally ribbed on one or two of the upper whorls, 

 with more often a varicose rib on one of the middle ones. The mark- 

 ings are as in the type, but more distinct, though many are colourless. 

 Sowerby figures a semi-ribbed shell as the type, a variation which does 

 not often occur, and it is minus the labial rib ; he does not figure the 

 variety. It is the R. similis of Brown according to his description, 



