1918.] Ekendranath Ghosh: Anatomy of Uniunidae. 117 



VI. Digestive Gland. 



The digestive gland forms a brownish mass round the stomach ; it 

 extends above and in front from the antero-dorsal aspect of the stomach 

 to the postero-dorsal angle of the anterior adductor muscle above the 

 oesophagus, and above and behind from the postero-dorsal aspect of the 

 stomach to the rectum ventrally ; the gland extends from the oesophagus 

 in front to the first loop of the intestine behind. In all species, except 

 Physunio ferrugivieus, the ducts of the gland are not clearly seen under 

 a magnification of ten diameters ; there are numerous tubular crypts 

 in the wall of the stomach into which the gland seems to open. 

 In Physunio ferrugineus the racemose nature of the gland is quite dis- 

 tinguishable under a magnification of 10 diameters, and the gland is 

 divisible into 4 lobes — one antero-dorsal, one postero-dorsal, and 2 

 ventral. A long duct from each lobe is distinctly seen to open into 

 the cavity of the stomach. 



VII. Vascular System. 



The vascular system has been studied in LanK'llide'ns marginalis by 

 injecting the blood vessels with a coloured fluid through the ventricle, 

 as living and fresh specimens are available. In other forms only the 

 heart, the vena cava, and a few other vessels could be studied properly. 



(a) Pericardium. — In Lamellidens and Physunio the pericardial 

 sac is elongately oval, with rounded ends ; the sac is slightly more 

 flattened in Lamellidens than in Physunio. In Solenaia the sac is 

 narrow and elongated, the anterior end being flattened from above down- 

 wards. A distinct gap is seen between the posterior end of the peri- 

 cardial sac and the dorsal aspect of the posterior adductor muscle in 

 which the rectum is placed, being surrounded by connective tissue. In 

 all a longitudinal fold of integument rises vertically upwards from the 

 inid-dorsal line of the wall of the pericardium ; this is only slightly 

 marked in the case of Lamellidens and Solenaia, being more prominent 

 in the latter behind the pericardium and over the posterior retractor 

 and anterior half of the posterior adductor muscle. In Physunio this 

 membrane is extraordinarily developed, and is prolonged as a thin 

 median flap between the dorsal wings of the two valves. The reno- 

 pericardial aperture is placed on the ventro-lateral aspect of the rectum 

 as the latter enters the pericardial sac. 



(6) Heart. — The ventricle in Lamellidens seems to be biloljcd when 

 it is fully expanded and placed in the middle of the pericardial sac 

 (occupying about the middle-third of the entire length of the sac) ; it is 

 bounded in front and behind by the bulbous swelling round the rectum. 

 In Physmiio the ventricle is placed close to the posterior end of the 

 pericardial sac. in Solenaia it is about half the length of the pericar- 

 dium and is placed in the middle of the sac. 



The auricles, right and left, are placed at the sides of the ventricle. 

 Each auricle in Lamellidens is triangular in shape, with the apex directed 

 forwards. The outer side is attached to the conjoined margin of the 

 inner lamella of the outer and outer lamella of the inner gill, just external 

 to the dorsal aspect of the kidney. It is attached to the ventricle in 



