MARSHALL: ADDITIONS TO "BRITISH CONCHOLOGY." 125 



Gregarious under stones at very low water at Guernsey and Herm, 

 where I have taken from 30 to 60 specimens under each stone in 

 suitable localities; it is confined to very narrow and limited areas, 

 where no other species appear to live with it. This forms one of the 

 staple shells of Guernsey sand, but it is very scarce at Jersey; nor does 

 it appear to be an abundant species anywhere else. 



A dwarf form is not uncommon, about one-third the size of type, 

 which is the var. minor of Philippi, and probably the male, as it is 

 found everywhere with the type, though in smaller numbers. The var. 

 hirta of Monterosato differs from this dwarf in being narrower, which 

 gives the shell a more oval outline, and it has two instead of three 

 riblets on the penultimate whorl. It was probably a specimen of the 

 latter which Jeffreys named var. paupercula. The type is one of the 

 most uniform of shells, no difference except that of size being 

 apparent in hundreds of specimens. An example from Guernsey has 

 the tubercle on the pillar-lip abnormally developed. 



R. calathus F.H.— Scilly Isles (Burkill and J.T.M); Lismore 6 f., 

 and Lynn of Morven, 40 f. (Knight) ! Knapdale Lochs, 11 t. ; Kyles 

 of Bute, 20 f. ; Eigg Island, 20 f. ; Iona, 1 6 f . ; Sound of Sleat, 20 — 

 50 f. ; Loch Inver, 25 f . ; and Loch Boisdale, 30 f. (Somerville and 

 J.T.M.) ; Torbay; Caldy Island; Freshwater West; Bantry Bay; 

 Connemara ; Killala Bay ; Oban, 25 f. ; Loch Broom, 30 f. ; Minch, 

 off Barra, 30 f. ; Sutherlandshire. 



Although the sculpture is most variable, it is never quite so fine as 

 in R. reticulata ; nevertheless, I incline to Jeffreys' opinion that it is 

 only a variety of the latter. There is really no dividing line between 

 the two either in shape or sculpture, many specimens of R. calathus 

 being quite as oblong as R. reticulata, while many of the latter are 

 conical. I have never met with pronounced Hebridean examples, 

 although it occurs with and is quite as abundant as R. reticulata 

 throughout the Clyde and Hebrides. The most characteristic speci- 

 mens come from Plymouth, and the coarsest from Guernsey. R. 

 calathus was dredged by the 'Challenger ' off Fayal, Azores, in 450 f., 

 but, as Dr. Watson says, "the solitary Challenger specimen is in such 

 bad condition that the identification of it has been very difficult, and 

 in the end not altogether without doubt. The various identifications 

 of the foreign specimens of this shell seem to need careful revision." 1 



It is occasionally pure white, and, as in nearly all the Rissoce, it has 

 its dwarf form, which is one-fourth the bulk of the type. Both are 

 extremely abundant inthe shell sand of Herm. An oblong form from 

 the Channel and Scilly Islands, having very coarse sculpture and 

 convex whorls, resembles R. hispidula Mtros., and that shell resembles 



1 ' Challenger ' Gasteropoda, p. 592. 



