BLOOMER : ON THE BRITISH SPECIES OF THE GENUS SOLEN. 39 



ever, its continuity is more complete, and it is also more developed, 

 forming the proximal end of the siphon. 



Along the whole dorsal surface of the animal is a muscular integu- 

 ment (PI. ii, fig. I, Int. D.), consisting of transversely crossed muscles; 

 these are further crossed and intertwined with longitudinal muscles of 

 the raised and fluted portion along the median line. The integument 

 is joined to the pallial muscles of the anterior and posterior ends, 

 and is also connected with the posterior adductor and retractor 

 muscles, the dorsal portion of the foot, and the teeth of the hinge 

 of the shell valves. Behind the posterior adductor muscle it is 

 much more developed and is attached laterally to the valves, in 

 consequence of which it appears as a continuation of the posterior 

 adductor muscle. 



The anterior adductor muscle (PL ii, fig. i, A. A.), is an extremely 

 broad plate of muscles, extending from a position a little anterior to 

 the mouth to the pallial muscles, bordering the pedal aperture, to 

 which it is united. 



The posterior adductor muscle (PI. ii, fig. i, P. A.), is also plate- 

 shaped, but is not nearly so wide as the anterior adductor. It is 

 connected on its anterior side with the retractor pedis posterior (PI. ii, 

 fig. I, P.R.P.), while on the opposite side it joins the circular mus- 

 cular growth supporting the siphon. Over and connected with it, 

 runs the dorsal muscular integument. 



ii. The Pedal Muscles. — The foot is a narrow and elongated body, 

 somewhat flattened laterally with a tendency to be keeled ventrally 

 and grooved dorsally. In it are three kinds of muscles. The first 

 consisting of longitudinal, the second of circular and semicircular, 

 and the third of transverse and oblique muscles, the whole being 

 enclosed in a muscular integument. When examined in detail, there 

 are seen on each lateral side two groups of longitudinal muscles (PI. 

 ii, fig. I, and PI. iii, fig. 5, Lo.M.) which traverse the whole length of 

 foot, and between each of these groups is a semicircular band, passing 

 from the dorsal to the ventral surface (PI. ii, fig. 5, Sem.M.). Bordering 

 the dorsal and ventral surfaces of the pedal cavity, are two rows of 

 bundles of transverse muscles (PI. ii, fig. i, and PI. iii, fig. 5). The 

 ends of these bundles spread out and their fibres pass between the 

 inner longitudinal muscles, to the inner sides of the bands of semicir- 

 cular muscles, while from the outer sides of these bands, muscular 

 fibres or oblique muscles (PI. iii, fig. 5, Oh.M.) pass in greater numbers, 

 between the outer longitudinal muscles to the muscular integument. 

 Towards the distal end of the foot these semicircular muscles gradu- 

 ally come together, first ventrally, then dorsally, and eventually form 



