194 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



(lemi-branclis begin more posteriorly than the inner ones. The 

 exterior edges at the bases of the gills are connected with the siphonal 

 wall, and the interior ones are joined together. The labial palps are 

 short at the base, and form a long taper to the distal ends. 



Musculature. 



1. Pallial Muscles. — The muscles of each mantle-lobe commence 

 over the anterior adductor muscle as a shallow band, and deepen as 

 they proceed to the ventral surface, along which they form a band of 

 considerable yet varying depth. 



The muscles of the proximal portion of the siphon are very strongly 

 developed, and terminate anteriorly in extremely powerful siphonal 

 retractor muscles. Inside each mantle-lobe, a short distance dorsal to 

 the line of concrescence, is a muscular ridge (Fig. 1, P.R.). This 

 ridge continues along the proximal portion of the siphon as far as the 

 siphonal retractor muscle. Its function is not apparent. 



The anterior adductor muscle (Fig. 1, A. A.) is a narrow and deep 

 muscular plate, widening towards the ventral surface. Posteriorly it 

 rests against the clavicle or rib of the shell. Dorsally and anteriorly 

 it is connected with the mantle-lobes, and posteriorly with the dorsal 

 and ventral integuments. 



The posterior adductor muscle (Fig. 1, P. A.) is an oval plate of 

 muscles. On the antero-dorsal surface rest the distal parts of the 

 bifurcations of the retractor posterior muscle. Dorsally the muscle is 

 connected with the dorsal integument, and ventrally with the ventral 

 integument. 



2. Pedal Muscles. — Though a portion of the distal end (Fig. 1, R.F.) 

 is missing, the general structure of the foot appears to be very similar 

 to that of Solen. 



The muscles apparently coinciding with the protractor pedis 

 anterior muscles are short and powerful. They pass anteriorly along- 

 side the viscera. Laterally they are attached to the valves of the 

 shell, while anteriorly they are joined to the dorsal and ventral 

 integuments. The fibres pass over the longitudinal muscles of the 

 foot "(that is, they are exposed to the pedal cavity), and spread out as 

 they proceed ventrally. 



The retractor pedis posterior muscle (Fig. 1, P. P.P.) is of medium 

 length, the distal end is bifurcated, and the bifurcations rest on the 

 posterior adductor muscle. The fibres of the muscle pass anteriorly 

 along the foot as longitudinal muscles. 



The retractor pedis anterior muscles are situated at the antero- 

 dorsal part of the foot. The free portions run dorsally close to the 

 liver, and are attached to the shell. The fibres on reaching the foot 

 pass partly into the pedal integument, and partly along the fibres of 

 the retractor pedis anterior muscles. 



Alimentary Canal. 



The lips (Figs. 2 and 3, A.L. and P.L.) are broad and thick. The 

 oesophagus (Figs. 2 and 3, Oe.) is long, and proceeds with a curve in 

 a dorso-posterior direction to the oesophageal division of the stomach 



