372 
MARSHALL: ADDITIONS TO “BRITISH CONCHOLOGY.” 
a small parasitic crab; but a subsequent examination of 
a score of living specimens of var. ¢runcata did not disclose 
the cause of these curious frettings, although they were 
present in every specimen. Perhaps they may be caused 
by an epidemic disease, for they are not present in any 
other species or variety of Donax that I have seen. 
The type ‘“‘is very common.at Paignton, South Devon, 
living in the sand, and bearing a curious mark of distinc- 
tion—small tufts of green ulve are frequently met with 
between tide-marks, growing apparently out of the sand, 
and these on examination are found to be rooted on the 
shells of Donaces, whose cool retreats are thus revealed 
alike to shell collectors and sea birds, the latter keen as 
man to detect the sand-dwelling conchifers.”—(Pidgeon). 
D. trunculus L.—Jeffreys’ figure presents no difference from 
that of D. vittatus; it should be more abruptly truncated 
at the anterior end, and his D. witfatus a little more 
oblique at that part. 
D. politus Polii—Poole, Dorset (Cooper) !; Weymouth Bay, 
rare. 
Half-grown specimens are beautifully marbled, but the 
markings tone down in the adult stage. Sometimes the 
ray is slight or evanescent, and a specimen from Guernsey 
has this characteristic ray broken up into a dozen fine 
ones, arranged as in Ze/dina donacina. 
Amphidesma castaneum Mont. — Scilly Islands, 4o f. 
(Smart and others), mostly valves. In one spot these 
valves may be dredged in thousands, but perfect speci- 
mens are rare, although I have several dozen immature 
ones. It was dredged by the ‘Challenger’ off Teneriffe, 
70 f., and off the Azores, 450 f. and 1000 f. It is variable 
in length and breadth and in the position of the beaks. 
A white form occurs at Scilly, as well as another which is 
abnormally oblong. 
(To be continued ). 
J.C., viii., Apr. 1897. 
