40 BLOOMER : ON THE BRITISH SPECIES OF THE GENUS SOLEN. 



a continuous circular band. Afterwards they and the transverse 

 muscles, which become irregular in their distribution, fray out, and 

 the whole form a network of muscular fibres. 



At the proximal and posterior end of the foot is the retractor 

 pedis posterior muscle (PI. ii, fig. i, P.R.P.), which, prior to its attach- 

 ment to the valves of the shell, bifurcates and forms the right and 

 left muscles. 



At the anterior end of the proximal portion of the foot are the 

 retractor pedis anterior muscles (PI. iii, fig. i, P.R.A., P.R.A'.). Each 

 of these is a long rounded muscle passing from the foot along 

 the ventral integument, and on leaving this, the muscle bifurcates, 

 the two portions then passing through the liver and dorsal integument 

 to the shell. The posterior bifurcation is the shorter one and it passes 

 directly to the valve. The anterior one is much longer, and passes in 

 an oblique direction over part of the anterior adductor muscle to the 

 valve. At its junction with the foot, the fibres spread out and pass 

 directly on the inside of the longitudinal muscles to the ventral and 

 ventrolateral surfaces. 



On each side of the foot a muscular band (PI. ii, fig. i, P.P.) 

 runs along the anterior ventral integument, in close proximity to the 

 anterior retractor pedis, to the anterior adductor muscle to which it is 

 attached, but has no connection with the shell. Possibly this repre- 

 sents the protractor pedis anterior, as I have been unable to trace any 

 other muscle likely to correspond to it. 



The dorsal part of the foot has also on each side, a slight muscular 

 connection (PI. ii, fig. i, P. El.) with the muscular dorsal integument, 

 but it has no attachment to the shell, and so fiir as I have been able 

 to ascertain, this is all that remains of the muscle representing the 

 elevator pedis. 



Solen siliqua, L. 



The muscular system in every way resembles that of S. en-^is, and 

 does not call for any special comment. 



Solen marginahts, Pult. and Don. (PI. ii, fig. 4). 



In comparison with S. ensis, the muscles in this species are much 

 more powerfully developed. The pallial muscles are wider and thicker, 

 and at the posterior end, the circular portion carrying the siphon is 

 considerably wider and more strongly built. The anterior adductor 

 mu.scle is not nearly so broad, while the posterior adductor is normal. 

 The free portion of the retractor pedis anterior is much shorter, the 

 bifurcated parts lie much closer together, and the fibres crossing the 

 foot pursue a more posterior direction, and pass underneath instead 

 of over the longitudinal muscles, and are embedded in the muscular 



