6 PROCEEDINGS OF TOE M ALACOLOGICAL SOCIETY. 



The muscular band of the pallial edge does not vary much in deptli, 

 but is soniewliat shallower at the posterior end, and the transverse 

 niuscle-hbres have the usual radial direction. The latter become more 

 developed near the posterior part of the ])edal aperture and increase in 

 tliickness towards the siphon. The longitudinal muscle-fibres, forming 

 the circumpallial muscles, also increase in number from the same region. 

 The siphon is muscular and compact. 



Pedal Muscles. — The protractor pedis anterior muscles (Fig. 1, P.P.) 

 are long and connected with the anterior adductor muscle, whilst 

 proximally their fibres lie close to the pedal integument. 



The retractor pedis anterior muscles (Fig. 1, P.R.J.) are long, flat, 

 very wide, and bifurcated ; each bifurcation is divided, the anterior 

 into two and the posterior one into three parts. They extend over 

 the greater ])ai't of the anterior adductor muscle with their distal ends 

 inserted into the shell. Proximally tliey pass inside the longitudinal 

 muscles of the foot in a fan-shaped direction. 



The retractor pedis posterior muscle (Fig. 1, P. P.P.) is long, but 

 not bifurcated. It is attached to the posterior adductor muscle, and 

 laterally is also inserted into the shell. Proximally its fibres pass 

 longitudinally along the foot. 



Alimentary/ Canal.— The mouth (Fig. 1, M.) is on the ventral 

 surface to the rear of the ajiterior adductor. The oesophagus, which 

 is short, proceeds dorsally with a slight curve, where it joins the 

 CBsophageal division of tlie stomach. This division is separated from 

 the cardiac one, which lies dorsally to it, by a lateral process of the 

 gastric Avail from its left side, and extends about half the length of 

 the stomach. Tlie pjdoric division is the largest one, and on the 

 postero-ventral side is continued as the caecum of the crystalline style 

 (Fig. 1, C. C.) ; the latter passes Avith a curve near to the ventral edge 

 of the foot. Tlie intestine (Fig. 1, In.) also leaves the pyloric division 

 in front of the caecum, but a little to the left. It then passes near to 

 the distal end of the caecum. There it makes a number of folds, then 

 proceeds below the caecum, turns dorsall)', passing close to the posterior 

 pedal wall to the dorsal part, where it turns posteriorly, going over 

 the posterior adductor muscle into the exhalent siphonal chaniher. and 

 ends in a conspicuous anus. 



The branchicB along the gill axis arc; separate from each othei'. The 

 lamellae are heterorhabdic and plicate. There are about seventeen 

 filaments to a plica in the inner, and fourteen in the outer demi-branch. 

 The frontal ridge of the principal filaments is sharp. 



Nervous System. — The cerebro-pleural ganglia are situated just in 

 front of the mouth, one on each side, and each ganglion gives off 

 anteriorly a nerve which passes to the lateral posterior edge of the 

 anterior adductor muscle; this divides and innervates the muscle and 

 the mantle. 



The viscero-parietal ganglia are situated at the antero-ventral edge 

 of the posterior adductor muscle, and each ganglion gives off posteiiorly 

 a nerve, the branchial nerve, which passes directly to the gill, and 

 another nerve which goes obliquelj' across the muscle, innervating it, 

 the siphon, and the mantle. 



