42 BLOOMER : CLASSIFICATION OF THE GENUS SOLEN, LINNE. 



It will, therefore, be assumed that the points not hereafter mentioned 

 are the same ?s in S. ens is. It resembles S. marginatus in the follow- 

 ing points: — In the strong development of the pedal muscles. The inner parts 

 of the bases of the gills are joined together. The fibres of the retractor pedis 

 anterior muscles cross the foot under, instead of over, the longitudinal ones. 

 The long oesophagus and position of the stomach. The shape of the 

 anteror part of the stomach. The length and direction of the caecum of 

 the crystalline style. In possessing only one circumpalhal nerve. 



The features by which it differs both from S. ensis and S. marginatus 

 are : — The hinge of the shell is situated some distance from the anterior 

 end, and the anterior part of the anterior adductor muscle, together with 

 the dorsal integument, terminate there. What represents the fourth 

 aperture is present at the posterio-ventral part of the pedal aperture. The 

 presence of a supra-pedal chamber at the anterio-dorsal end. The large 

 pyloric portion of the stomach, and of tlie proximal part of the caecum 

 of the crystalline style, and the absence of folds in the intestine shortly after 

 leaving the stomach. The numbers of branches of the anterior pallial 

 nerve, which are more than in ;S'. marginatus, but fewer than in S. ensis. 



It is admitted that the type of the genus Solen is ^S*. vagina, Linne *^', 

 and it is evident that the anatomical differences between -S'. vagina and 

 S. ensis and siliqua prevent the two latter being placed in the same genus. 

 In the recent classification ''' these two species have been placed in the 

 genus Ensis, Schumacher, and I do not see any reason Avhy this should 

 be altered. That there are distinctive, and what I have found to be con- 

 stant, characters, I think I have shown, thus justifying them being treated 

 as separate species, and not varieties. There now remains S. pelhwidus. 

 This animal I have endeavoured to demonstrate possesses some characters 

 common to S. ensis, some common to S. vagina, and others possessed 

 by neither of them. It, therefore, follows that S. pellucidus cannot be 

 placed in the genus Solen or Ensis. In the before-mentioned classifica- 

 tion it has been placed in the genus Cultellus, Schum., and as I have 

 not been able to see the type animal of Schumacher's genus (C magnus), 

 I cannot at present say if anatomically this is correct or not. 



I look upon Solen vagina as a more primitive form, and upon Ensis 

 ensis and E. siliqua^as more specialised forms — perhaps E. ensis slightly 

 more so than the E. siliqua ^fiitii Cultellus j^/ellucidusJ coming somewhere 

 between S. vagina and E. siliqua. I do not, however, suggest that any 

 one species has directly originated from the other. Perhaps the following 

 tree will better illustrate what I wish to convev : — 



1 British Conchology, Jeffreys. 



1 A History of British Mollusca and their shells. Forbes and Hanley. 

 1 Synopsis of the Solenidae of North America and the Antilles. Ball. 



2. List of British Marine Mollusca prepared by a Committee of the Conchological Society of 

 Great Britain and Ireland. 



