1918.] Ekendranatti Giiosit : Anatoiny of Unionidae. 113 



glandular portion of the kidney and to the outer lamella of the inner 

 2,111 behind the visceral mass and foot, from beneath the posterior ad- 

 ductor muscle. 



(3) The outer lamella of the mner gill is similar to the preceding in 

 its mode of attachment. 



(4) The inner lamella of the inner (/ill is attached to the side of the 

 base of the visceral mass and behind it to the inner lamella of the oppo- 

 site inner gill to form the floor of the cloacal chamber. In Lamcllidcns 

 the attached dorsal margin of the inner lamella is placed just below the 

 glandular portion of the kidney, but towards the posterior end of the 

 visceral mass it is displaced downwards from the kidney, so that the 

 inner wall of the inner suprabranchial chamber in this region is formed 

 by a portion of the side wall of the visceral mass ; in Solenaia the case 

 is exactly similar to that in Lamellidens. In Physunio the attached 

 margin is placed beneath the glandular portion of the kidney near the 

 posterior end of the visceral mass, where it is suddenly displaced down- 

 wards, as in the other forms. 



Suprabranchial canals. — (a) The outer suprabranchial canal is placed 

 on a higher level than the inner in Lamellidens and Physunio, but on a 

 lower level in Solenaia. In Lamellidens the canal is small in the bccin- 

 ning, but gradually widens out posteriorly and opens into the cloacal 

 chamber on the undersurface of the posterior adductor muscle in the 

 middle of its antero-posterior thickness. Elongately triangular ante- 

 riorly, it widens out into an equilateral triangle behind in transverse 

 section. In Physunio the canal is elongated and slit-like in front, but 

 elongately triangular (with base directed upwards) behind the visceral 

 mass in transverse section ; it ends in the cloacal chamber at the anterior 

 end of the ventral aspect of the posterior adductor muscle. 



In Solenaia the canal is triangular in front, but quadrilateral at the 

 posterior end of the visceral mass in transverse section, and terminates 

 in the cloacal chamber in the middle of the antero-posterior length of 

 the ventral aspect of the posterior adductor muscle. 



ih) The inner suprabranchial canal in both Lamellidens and Physunio 

 is slit-like in the beginning, becomes triangular posteriorly in transverse 

 section and is nearly of the same height in its entire length. In Solenaia 

 the canal is also slit-like in the beginning but becomes quadrilateral in 

 transverse section at the end of the visceral mass ; it is, however, of 

 greatest width (from above downwards) anteriorly, forming about half 

 the width of the inner gill, but becomes less so posteriorly. 



The rencd aperture is placed in the inner suprabranchial canal ; in 

 Lamellidens and Physunio at about the junction of the anterior one- 

 third and posterior two-thirds of the line drawn from the anterior end 

 of the inner gill to the posterior end of the visceral mass. In Lamellidens 

 the aperture is slit-like and placed longitudinally, with a thick white rim ; 

 in Physunio it is rounded and without any thick white margin. In 

 Solenaia it is slit-like and placed longitudinally some distance behind 

 the middle of the length of the visceral mass. 



The genital aperture is placed below and a little in front of the renal 

 aperture in the same canal in both Lamellidens and Physunio. In 

 Solenaia the aperture could not be made out. 



c 



