270 cardiidjE. 



they are sometimes marked with concentric zones of a 

 paler colour than the rest of the shell, denoting the 

 lines of growth. This state is the C. spinosum of J. 

 Sowerby. C. ciliare of Montagu represents an earlier 

 stage of growth : Linnets species of that name is very 

 different. Turton noticed and figured in his ' Con- 

 chylia Dithyra' (p. 181, tab. 13. f. 7) a distorted shell, 

 obliquely twisted to the posterior side which is more 

 elongated or produced than usual. The cardinal teeth 

 in this specimen are equal in size, tubercular, and 

 slightly cloven ; there is a third cardinal in the right 

 valve, and the laterals are very short. Linne supposed 

 that the present species was perhaps a variety of C. 

 echinatum ; but the latter is much smaller, more solid, 

 and never angular, and it has shorter prickles. The 

 posterior gape, also, in C. aculeatum is very considerable, 

 while in C. echinatum it is scarcely perceptible. 



2. C. echina'tum *, Linne. 



C, echinatum, Linn. Syst. Nat. p. 1122 ; F. & H. ii. p. 7, pi. xxxiii. f. 2, 

 and (animal) pi. N. f. 3. 



Body somewhat compressed, varying in colour from yel- 

 lowish-white to a rich pink : mantle open for three-fourths of 

 its circumference, having a plain and thin margin (which in 

 the young is dentate or notched) about a line in breadth, 

 behind which it is suddenly thickened, and at regular intervals 

 raised into a series of glandular warts or tubercles, corre- 

 sponding with the grooves inside the shell : tubes contiguous, 

 each encircled with a fringe of white cirri or tentacular pro- 

 cesses, which have at their base a corresponding row of yellow, 

 brown, or red points ; the outside of the tubes is also clothed 

 with some scattered and coarse white pendulous filaments; the 

 excurrent tube is rather the shorter and smaller of the two, 

 and its orifice is provided with a globular valve, which is occa- 

 sionally protruded : mouth very large and funnel-shaped : gills 



* Prickly. 



