gS BLOOMER : ON THE CRITISH SPECIES OF THE GENUS SOI.EN. 



anterior division of the posterior pedal sinus bifurcates and communi- 

 cates with the sinus lying over the anterior adductor muscle (A. A. S.), 

 this sinus extends posteriorly over the viscera and laterally down the 

 sides of the same. 



The sinus of the viscero-parietal ganglion {V. P. S.) is situated 

 between the bifurcated parts of the posterior retractor pedis muscle 

 and the posterior adductor muscle, and dorsal to the viscero- 

 parietal ganglion. 



The venous system in the mantle does not possess well-walled 

 passes, but being very lacunous and very soft it is capable of receiving 

 an enormous cjuantity of blood. In its posterior part the venous 

 blood mixes with the arterial, and collects in the pallial sinus. I'he 

 siphonal tentacles exhibit large lacunae opening directly into the 

 siphonal sinus {Si. S.). The afferent branchial vessel (A. B. V.) 

 originates from the sinus of the viscero parietal ganglion {V.P.S.). 

 The efferent branchial vessel {E. B.V.) conveys the arterial blood to 

 the auricle (^-1?/.), opening into it at the posterior end, and as tlie gills 

 extend a little anterior to this part of the auricle, the vessel has con- 

 sequently, one portion of it anterior and the other posterior to the 

 point of junction. 



Sulen ailifjua, L., and SoJcn ma nj in edits, Tult. and Don. 



There is nothing calling for comment in the venous system of 

 these species. 



The Heart. — This is typical of the Pelecypoda, a median fusiform 

 ventricle and lateral triangular auricles. 



Arterial Sijiifem. — Salen ensi.-<, L. 



Arising from the anterior end of the ventricle is the anterior aorta 

 (A. Ao.), it proceeds dor.sally over the viscera and shortly gives off an 

 artery which passes to the wall of the pericardium, from there to 

 the sinus of the foot, and then to the kidney. The anterior aorta in 

 its passage forward gives off various hepatic or gastric branches, and 

 on reaching a position dorsal to the mouth it curves in slightly and 

 then descends perpendicularly. At the point of incurving it. sends 

 off a branch to the anterior portion of the right lobe of the liver 

 (A. A. M.), after leaving this organ, the branch passes over the ante- 

 rior adductor muscle to the region of the hinge teeth of the shell ; 

 its further course has not yet been traced owing to the injury always 

 caused to this part of the animal in its removal from the shell. 



During the descent of the anterior aorta, a large artery is given 

 off, the visceral artery {A.V.), which vascularises a large portion of the 

 viscera. Two branches of it pass along the caecum, of the crystalline 

 style and cover the latter with their fine ramifications. The largest 

 branches, however, pass on to the intestinal folds and terminate there. 



