JOURNAL OF CONCHOLOGY. 385 
ADDITIONS TO “BRITISH CONCHOLOGY.” 
By J. T. MARSHALL. 
(Continued from page 372.) 
Amphidesma castaneum var. subtrigona Monts. 
(Nomenclatura, p. 27, as var. mnor-subtrigona—New to 
Britain. Smaller and almost triangular. This is the 
normal form at Guernsey and Herm, and it is occasion- 
ally met with at Scilly and the Land’s End. Jeffreys’ 
generic figure is different from that of his plate figure ; 
but the latter is correct. 
Mactra solida L.—Exmouth, very large and solid—z in. by 
1? in. . 
Var. truncata Mont.—Guernsey Harbour. 
Var. elliptica Brown.—Epidermis conspicuous and_per- 
sistent. Sowerby’s figure is the var. ¢fermedia, and not 
this. 
M. subtruncata DaC.—Dredged specimens are usually fully 
covered with the epidermis, but when taken from between 
tide-marks it appears on the sides only. The largest come 
from Southport, and are rd} in. by 1 in. 
Var. striata Brown.—Guernsey : Torbay ; Weymouth. 
Analogous to and resembling JZ. solida var. truncata, 
but this variety has the lunular areas more sharply and 
deeply defined. 
Var. ingequalis Jeff.—Torbay ; Southport. 
Var. tenuis Jeff.—Torbay ; specimens having the characters 
of this variety, but broader instead of longer. 
Mr. Alfred Brown relates of this species that two of 
the ‘“carnivora” will attack opposite sides of the same 
bivalve, and on one occasion he noticed “a singular case 
of defective instinct in a Purpura, which was diligently 
piercing a hole in a single valve (a much-worn one too) of 
Mactra and had nearly completed its task when interrupted !” 
1. Mollusca of the Firth of Clyde, p. 33. 
31/5/97 Z 
