MARSHALL : ADDITIONS TO " BRITISH CONCHOLOGY. I37 



everywhere together, as they would be if the two sizes indicated the 

 sexes, but specimens of all sizes, from the dwarf of half-a-line to com- 

 parative giants a third-of-an-inch, are indifferently keeled or rounded 

 at the base. The authors of "British Mollusca" say 1 — "The var. 

 stagnalis of Brown, which is usually termed subunibilicata by col- 

 lectors, but which does not agree with Montagu's description of that 

 species, is smaller and shorter than the type, more convex in whorls, 

 basal inclination and general outline .... Professor Brown 

 sent us similar shells as Paludina stagnalis Menke." Brown's figures 

 of Turbo stagnalis will do for anything, and Searles Wood's descrip- 

 tion and figures (as Paludestrina subunibilicata) apply to H. ventrosa, 

 though he says it comes between that species and H. ulvce. 2 



Var. albida Jeffr. — Skegness, fine and not uncommon. 



Var. barleei Jeffr. — Torbay ; Skegness ; Glengariff. Also Faerce 

 Channel, 570 f. ('Triton')! Bay of Biscay, 1,062 f. ('Travailleur' 

 Expedition). Fossil in the Belfast deposit (Praeger) ! This shows 

 some considerable variation, and I have half-a-dozen different forms 

 of it. It is well figured by Jeffreys and Sowerby. It is curious to 

 note that this variety, although living in the littoral zone, is constantly 

 turning up in the dredge from various depths. Sea-birds would sug- 

 gest the source were it not that the type form swarms in estuaries and 

 constantly serves as food for birds, but is not found on the ocean- 

 bed like this variety. An analogous case occurs in Lepton clarkice, 

 which is never taken alive except from sea-weeds in rock-pools, yet 

 has often been dredged at various depths, in one case in 690 fathoms 

 in the Atlantic, 150 miles off the Scillies. 



Var. octona L. — More slender throughout, with a narrow base. 

 Bundoran, and dredged in Donegal Bay by the 'Porcupine.' This 

 peculiar variety occurs in the same pond at Guernsey with H. ventrosa 

 var. elongata, and closely resembles it ; in fact, some specimens can 

 be assigned to either variety, and I am inclined to consider both 

 forms a hybrid between H. ulvce. and H. ventrosa. I have often 

 visited their habitat, which is a natural lake on a small private estate 

 adjoining the sea-shore, having a natural spring in the centre, and into 

 which the sea flows and ebbs at every tide. It abounds in mullet and 

 other sea fish, with a few marine mollusca, and is a more marine 

 environment than is usually occupied by H. ventrosa. 



Var. minor Marsh. {J. Conch. , vol. 7, p. 252). — In many places 

 on the open sea-coast, under stones between tides. This is the shell 

 mentioned in "British Mollusca" as "a small variety taken in Torbay 

 narrower than usual," etc. There are quite half-a-dozen forms of it. 



1 Vol. 3, p. 141. 



■? Crag Moll. j vol. i, p. 10S, pi. xi., f. 2a, b. 



