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ON THE ANATOMY OF UNSIS MACHA, SOL EN FONESII, 

 AND S. VIRIBIS. 



By H. H. Bloomer. 



Bead lOth November, 1905. 



By the kindness of Professor E. Ray Laukester, F.R.S., Director of 

 the British Museum, and Mr. Edgar A. Smith, I.S.O., I have been 

 enabled to examine the following species : — 



1. Ensis MACHA, Molina. 



^. macha resembles E. emu, but is more massively built. It is 

 comparatively shorter, broader, and deeper. The edge of the posterior 

 end of the proximal portion of the siphon is quite straight, while in 

 £. ensis it curves a little anteriorly at the centre. The fourth 

 aperture is longer, and situated nearly in the centre of the ventral 

 surface ; in E. ensis it is more posterior. 



The muscular flaps enclosing the pedal aperture are larger and 

 curve more inwardly than in E. ensis. 



The anterior adductor muscle is not so broad, but has a greater 

 increase in depth towards the posterior end. The distance from the 

 posterior adductor muscle to the end of the proximal portion of the 

 siphon is not so great as in E. ensis. In the free portions of the siphon 

 (which are longer than in E. ensis) the walls of the two chambers are 

 concresced for some distance. The tentacles bordering the siphonal 

 apertures are not nearly so numerous as in E. ensis. 



Internally, though the alimentary canal resembles that of E. ensis, 

 the fore-part of the stomach is different. The central cavity is 

 situated more anteriorly, the pyloric division is larger, and the i 

 (Esophageal and the cardiac divisions are smaller. The muscular 

 ridge separating the two last-mentioned divisions, and which appears 

 as a continuation of the muscular papilla, is much more pronounced, 

 wliile the oesophageal division projects more anteriorly. 



2. SoLEN FoNEsiT, Dunker. 



Soleyi Fonesii resembles S. vagina. The following are the points of 

 difference : — 



The animal is proportionately shorter and deeper, the length being 

 only four and a half times the depth. The anterior edge of each 

 mantle-lobe is straight, not curved as in S. vagina, and runs a little 

 antero-ventrally. The muscular flaps of the pedal aperture are 

 broader and are capable of entirely closing it. Their exterior surface 

 is coloured a brownish black in the specimen examined ; a part of the 

 free portion of the siphon has been broken off, but what remains shows 

 the transverse ribbing to be finer and closer, and to be coloured the 

 same as the muscular flaps of the pedal aperture. A narrow band of 



