CLASSIFICATION OF THE BRITISH SPECIES OF THE 

 GENUS SOLEN, LINNE.^ 



By H. H. bloomer. 



Having recently described some of the chief features in the anatomy of the 

 species of Solen, 1 now purpose considering how they bear on the question 

 of the present classification. For this purpose it will be sufficient if I only 

 call attention to the chief points by which the other species differ from 

 S. ensis without going into the anatomy of the latter. 



The chief differences in S. siliqua are : — It is larger, and quite straight 

 along the dorsal surface. The oesophagus is straighter, and the divisions 

 of the stomach are more pronounced. The cardiac portion does not project 

 so far anteriorly, nor does the posterior end of the pyloric portion rise so 

 much dorsally, and the muscular papilla is more central. 



In S. warginatus the following are the chief points of dili'erence : — 

 It is straight along the dorsal surface. There is no fourth ;iperture, and 

 there are no labial grooves. The inner parts of the bases of the gills are 

 joined together. The free portion of the siphon is longer. The pallial 

 and pedal muscles are more developed. The free portion of the retractor 

 pedis anterior mu.scle is shorter, the bifurcations lie clo.se together, and the 

 fibres of it cross the foot in a posterior direction, passing underneath instead 

 of over the longitudinal muscles. The lips project anteriorly, the oesoph- 

 agus is longer and proceeds posteriorly to the stomach, the latter lying in 

 a more posterior position over the distal end of the foot. Tlie muscular wall 

 dividing the oesophagael from the cardiac portion is more developed, and 

 projects a considerable distance into the stomach, thus separating the 

 anterior part of these divisions from each other. The caecum of the 

 crystalline style is of considerable length, leaves the pyloric portion on its 

 ventral surface, curves, and passes in an anterior direction. The intestine 

 passes along the caecum, round the distal end, and returns along the other 

 side, and is connected with it for the greater portion of the distance. The 

 liver does not project anteriorly over the anterior adductor mu.scle. An- 

 teriorly each cerebro-pleural ganglion gives rise to only one nerve — the 

 anterior pallial nerve — which has one branch. There is only one 

 cvrcumpallial nerve. 



Solen pellucidus possesses some features of re.sem))lance to S. ensis, 

 some to *S'. marginatus, and others not common to either of these species. 



Read at a meeting of the Midland ilalacological Society. 



