C. 
MARSHALL: ADDITIONS TO “ BRITISH CONCHOLOGY.” 359 
Lundy Island, 60 f.; off the Smalls, Irish Sea ; West Ork- 
neys, 45 f. Also Atlantic off Scilly, 690 f. (‘Porcupine’)! 
When living in fine sandy mud the delicate sculpture 
of the ribs is beautifully preserved ; but when on coarser 
ground, the ribs are flatter and worn almost smooth. 
Specimens from Portmarnock are fine and clean, but 
without a particle of sculpture. It appears to be most 
abundant in the Sound of Sleat, from 25 to 95 fathoms, 
and in the Minch off Loch Boisdale in 18-—35 fathoms ; 
valves occur here in thousands. ‘The shell is wonderfully 
true to type, no variation being apparent in hundreds of 
specimens. 
norvegicum var. gibba Jeff.— Herm and Guernsey ; 
Weymouth Bay. 
Var. rotunda Jeff.—Shetlands (Jeffreys) ; Herm ; Torbay. 
Var. pallida Jeff.—Guernsey and Herm. 
Isocardia cor L.— Clyde between Cumbrae and Arran 
(Robertson and Somerville) ; off Mull, Lismore, and 
Sound of Sleat (A. Brown); Moray Firth (Scott and 
others) ; Aberdeen trawlers. 
The home of this species appears to be the Irish Sea 
and Bristol Channel, where it is somewhat plentiful. The 
degree of convexity and the outlines of the shell are ex- 
tremely variable, the latter character changing perhaps 
half a dozen times during the growth of the individual, as 
may be seen by observing the lines of growth, which have 
varying angles at various stages, so that many variations of 
form might be made out of it. Foran interesting paper 
indicating some of these forms, and illustrated with out- 
lines, by Mr. F. W. Wotton, see “‘Science Gossip,” Aug. 1894. 
Lsocardia does not become orbicular until fully adult, 
when the outer margins are added to and considerably 
thickened, with the addition of internal ribs and but- 
tresses. Many specimens, especially when half grown, are 
