Bl.UOMER : ON THE DRITlSH SPECIES OF THE GENUS SOLEN. 135 



be seen that in many respects the aHmentary canal more closely re- 

 sembles that of the latter than that of the former, the more important 

 differences being the relatively larger size of the pyloric portion of the 

 stomach and of the distal part of the caecum of the crystalline style, 

 and the absence of folds in the intestine shortly after leaving the 

 stomach. 



The position of the liver (Fig. i, L.) is similar to that of aS'. ensis. 



Nervous System. 



The nervous system of JS. pelluci(his resembles that of S. ensis, 

 differing from it, however, in the number and distribution of the 

 pallial nerves. 



The anterior pallial nerve only gives rise to two branches. The 

 first branch leaves the nerve after it has passed a little distance under 

 the ventral surface of the anterior adductor muscle, and the second a 

 short distance before reaching the anterior edge of the muscle ; both 

 branches cross the mantle lobe and join the circumpallial nerve. The 

 posterior pallial nerve does not give rise to any branch which crosses 

 the mantle lobe as in S. ensis 



There is only one circumpallial nerve, which anteriorly passes 

 along the dorsal portion of the muscular part of the mantle lobe, and 

 gradually attains a ventral position as it proceeds posteriorly. It is to 

 be observed that the two anterior pallial nerves fuse together close to 

 where the teeth of the shell are connected with the dorsal integument, 

 forming a small ganglionic mass, and then separating, pass along the 

 mantle lobes. 



Circulatory System. 



The general features resemble those of S. ensis, but owing to the 

 smallness of the specimens examined it has not been possible to follow 

 it out in all its detail. 



From the foregoing morphological account of the different species, 

 and from further work shortly to be published, I purpose at no distant 

 date to review the present classification of the genus ISolen. 



