1920.] E. Ghosh : Anatomy of the Solenidae. 49 



of its exact shape in preserved specimens in which the organ may 

 be fixed in any degree of contraction. The foot of CuUellus java- 

 nicus has been figured by Weber (50). who showed the different 

 shapes it can assume in dilTerent degrees of extension. 



The intrinsic pedal musculature as described by Bloomer (5), 

 and followed by me in my specimens, requires a brief notice in 

 order to understand the differences in the arrangement of the 

 muscles in the different genera. The pedal musculature consists 

 of (i) two layers of longitudinal muscles on each side (an outer, and 

 an inner abutting on the pedal cavity) separated by (2) a dorsi- 

 ventral semi-circular band; (3) two rows of transverse muscle 

 bands extending across the pedal cavity along its dorsal and ventral 

 'surfaces, and passing to the inner side of the semi-circular layers; 

 (4) a thin layer of circular muscles just beneath the epithelial 

 covering of the foot (the pedal integument of Bloomer) ; (5) lastly, 

 a set of oblique muscles extending from the pedal integument 

 between the outer longitudinal muscles to the outer side of the semi- 

 circular bands. 



The protractor pedis muscle is well developed in some genera 

 {Solecurtus, etc.) but rudimentary or absent in others {Solen, 

 etc.). 



The retractor pedis anterior muscle, one on each side, consists 

 of one or two bands which pass upwards to be attached to the 

 valve. The pedal portion of the muscle consists of radiating fibres 

 which spread out in the foot either on the inner side of or super- 

 ficially to the longitudinal muscles of the foot. They are of some 

 taxonomic importance in the differentiation of some genera. 



The retractor pedis posterior muscle bifurcates into right and 

 left portions which are attached to the corresponding valves. It 

 does not bifurcate in Cultellus cultellus, Dunker, The muscle at its 

 insertion may either remain separate from or merge into the fibres 

 of the posterior adductor muscle. The impression of the muscle 

 on the valve may be of different sizes in comparison with that of 

 the posterior adductor muscle. 



lyABiAiv Palps. The palps are wide and short, or narrow and 

 elongated. The anterior lips formed by the union of the outer 

 labial palps are either placed immediately behind the anterior 

 adductor muscle, or are removed posteriorly from the muscle. 

 A labial groove has been described by Bloomer (3) on the inside of 

 each mantle lobe passing dorsally from the fourth aperture 

 towards the foot. The distal portions of the labial palps are placed 

 in the groove. 



GiLivS. The gills are generally narrow (in depth), elongated, 

 and are often prolonged into the siphon. The outer lamella of 

 the outer gill (demibranch) is generally attached to the mantle 

 lobe along its dorsal margin. The inner lamella of the inner gill 

 is divisible into visceral and cloacal portions in consideration of 

 its attachment along its dorsal margin. The visceral portion is 

 generally free (except in Ensis), whereas the cloacal portion is 

 either free or joined to its fellow of the opposite side. Branchial 



