20 BLOOMER : ON THE P.RITISH SPECIES OF THE GENUS SOLEN. 



pallial nerve, but I have not been able to trace the complete 

 connection. 



The posterior portion of the outer circumpallial nerve joins the 

 anterior portion close to the fourth aperture (Fig. i8, F.A.). 



The inner circumpallial nerve proceeds from a branch of the 

 anterior pallial nerve, and passes in a curved direction to the posterior 

 pallial nerve. 



The outer circumpallial nerves and the nerves of the anterior 

 adductor muscle converge and apparently join at the point where the 

 dorsal integument is connected with the teeth of the shell (Fig. i8, 

 D.I.S.). 

 S. siliqua, L. 



The nervous system of this species is similar to that of S. ensis, 

 and only differs from it in minor details. 

 S. marginatum, Pult. and Don. 



The cerebro-pleural ganglia are not discernable through the 

 ventral integument, owing to the forward projection of the lips formed 

 by the labial palps. Anteriorly each ganglion only gives rise to one 

 nerve, the anterior pallial nerve. It proceeds to the posterio-lateral 

 edge of the anterior adductor muscle, then along the ventral surface of 

 the muscle near its lateral edge, but when about one-third of the 

 distance it divides, the inner branch continuing under the muscle, and 

 eventually reaching the point where the dorsal integument is attached 

 to the teeth of the shell. The outer branch passes along the 

 transparent portion of the mantle lobe, and joins the circumpallial 

 nerve. 



The pedal ganglia are similar in position to those of aS'. ensis, but 

 owing to the position of the viscera in the foot, a portion of the 

 intestine and the caecum of the crystalline style lie distal to them. 

 A number of nerves radiate from the ganglia to the viscera and the 

 muscles of the foot. 



The position of the viscero-parietal ganglia is discernable through 

 the transparent ventral integument as in aS'. ensis. Passing from them 

 posteriorly are two large pallial nerves, each of which, shortly after pass- 

 ing under the posterior adductor muscle, bifurcates, the inner branch of 

 the one converging towards the inner branch of the other, and both 

 proceed to the base of the siphon. The outer branch pursues a 

 ventro-lateral direction across the muscular portion of the mantle lobe. 

 Both nerves apparently join the circumpallial nerve, though I have not 

 been able to clearly trace the connection. There is evidently only one 

 circumpallial nerve, the same being equivalent to the outer 

 circumpallial nerve of S. ensis. 



