Th 
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196 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
also shown that in Cardium “ oblongum,’’ C. echinatum, 
and C’. rusticum a rudimentary byssus gland, corresponding 
in all respects to the structure above described, 1s present. 
Finally, Gwyn Jeffreys* mentions a case of C. edule itself 
in possession of a functional byssus. 
Of the apertures of the body, the mouth (M,, fig. 3) is a 
wide slit lying between the viscero-pedal mass and the 
anterior adductor; the anus (47.) lies on the dorsal surface 
of the posterior adductor. The apertures of the gonad and 
renal organ are rather difficult to observe. They may be 
seen by folding back the internal branchia (see fig. 3). The 
ureter (Ren’., fig. 4) 1s a mere slit in the wall of the 
renal vestibule, and lies on the lateral wall of the renal 
organ just dorsal to the origin of the posterior retractor 
muscles of the foot. The external opening of the gonad 
lies in nearly the same position, but on the lateral and 
posterior wall of the viscero-pedal mass; it is slightly 
elongated and sometimes has tumid lips. 
THE MUSCULATURE. 
The muscles may be conveniently arranged into four 
groups: (1) the adductor muscles of the shell; (2) the 
extrinsic muscles of the foot; (3) the intrinsic muscles of 
the foot; and (4) the pallial muscles. The extrinsic and 
intrinsic pedal musculature form really one system. The 
pallial muscles may be divided into the pallial muscles 
proper and the muscles of the siphons. 
(1) There are two adductor muscles of the shell (Add.a. 
and Add.p., fig. 3), anterior and posterior. Hach is a 
strong bundle inserted on the dorsal oblique surface of the 
shell near the margin, and running across in an exact trans- 
verse direction from valve to valve. Owing to the curve 
of the shell the scars of attachment (Add.a’. and Add.p’., 
* British Conchology, vol. IT., p. 208, 
