1918.] Ekendranatii Ghosh : Anafumy of Umoiiidac. 119 



adductor muscle. Each supplies the corresponding half of the pos- 

 terior adductor muscle, the posterior retractor muscle of its side and 

 the posterior portion of the rectum. 



The pallial sinus (vein) begins in the substance of the mantle flap 

 at the level of the inhalent aperture just behind the thick rim of the 

 lobe. It passes upwards and forwards in a curved manner below the 

 posterior adductor muscle and ultimately opens into the auricle of its 

 side at the postero-external corner. This sinus is also present in the 

 other two genera. 



The vena cava {median ventral sinus) at first lies between the two 

 glandular portions of the kidneys, but gradually shifts downwards in 

 its posterior course so as to lie at the point of union of the two glandular 

 and non-glandular sacs ; the ventro-lateral wall of the vena cava on either 

 side is perforated with a row of apertures, the openings of vessels from 

 the wall of the glandular portion of the kidneys ; they are distinctly 

 seen under a magnification of 10 diameters. In Solenaia and Phi/sunio 

 the relation between the vena cava and the kidney is similar to that in 

 Lamellidens. In Lamellidens and Solenaia the transverse section of 

 the vena cava is oval, with the short diameter vertical ; in Physunio 

 it is also oval but with the short diameter horizontal. 



The two afferent branchial veins lie along the line of attachment of 

 the inner lamella of the outer and outer lamella of the inner gill — in all 

 the three genera. 



The single afferent branchial vein lies along the base of the inner 

 lamella of the inner gill in all the three genera. It is interesting to note 

 that in Anodonta it lies along the base of the outer lamella of the outer 

 gill. 



VIII. Excretory System. 



The Jcidney is doubled on itself, as usual, and is divisible into (a) 

 glandular and (b) non-glandular portions. 



The glandular 'portion of the kidney lies beneath the non-glandular ; 

 at its anterior end it communicates with the pericardium and is separate 

 from its fellow by a distinct interval, and further behind by the inter- 

 position of the vena cava. In Lamellidens the sac is flattened from 

 above downwards in front, lying on the ventral aspect of the non-glan- 

 dular sac. Then the sac becomes oval in transverse section and, lastly, 

 towards the posterior end of the visceral mass it is twisted on itself 

 coming to lie on the inner side of the ureter, at first obliquely {i.e., with 

 the long diameter in a section placed downwards and outwards from 

 above) and then vertically. The vena cava is now placed beneath the 

 pericardial sac, with a small portion of the inner wall of ureter and 

 glandular sac laterally and further back with the glandular sac only, 

 the ureter being displaced to the outer side. 



In Solenaia the glandular sac is separated at first from its fellow of 

 the opposite side by the vena cava, and behind by the foot, which inter- 

 venes between the two. The inner wall of the sac is fused with the upper 

 portion of the side of the foot, while the non-glandular portion placed 

 dorsally at first is displaced to the outer side. 



In Physunio the glandular sac lies beneath the non-glandular portion 

 in the beginning, but is gradually placed on its inner side between it 



