118 Records of the Indian Museum. [Vol. XV, 



the middle third of its length. The auriculo-ventricular opening is a 

 slit-like aperture guarded by 2 semilunar valves, above and below. 

 There are 3 to 4 apertures inside the outer border of the auricle to receive 

 blood from the efferent branchial vessel. In Solenaia the auricle is 

 trapizoid in shape ; of the two parallel sides the short one is attached to 

 the ventricle and the long one to the gills. There seems to be a single 

 aperture to receive blood from the gills. In Physunio the shape of the 

 auricles is similar to that in Lamellidens ; the apertures inside the outer 

 side to receive blood from the gills are 4 or 5 (?) in number. 



The following blood vessels have been traced in Lamellideris by in- 

 jecting them with carmine (suspended in water) through the ventricle. 



The anterior aorta passes forwards along the dorsal aspect of the 

 rectum and reaches the posterior end of the digestive gland where it 

 divides into right and left viscero-pedal arteries. Each viscero-pedal 

 artery runs forward and a little outward into the substance of the super- 

 ficial portion of the digestive gland, and then curving downwards and 

 forwards gradually comes to reach the postero-ventral aspect of the 

 anterior adductor muscle at the corner of the mouth, where it divides 

 into two branches, pallial and palpal arteries. The pallial artery passes 

 forward in the substance of the mantle-lobe along the ventral margin 

 of the anterior adductor muscle to reach the antero-ventral angle of the 

 latter, where it divides into two branches again : the first, the dorsal 

 pallial artery, curves upwards and backwards along the anterior margin 

 of the anterior adductor muscle (in the substance of the mantle lobe), 

 supplying small arteries to that portion of the mantle which lies in front 

 of the muscle and to the muscle itself ; the other, the anterior pallial 

 artery, curves downwards and backwards and then runs backwards along 

 the dorsal aspect of the thick rim of the mantle lobe, to the posterior end 

 near the inhalent margin where it seems to divide into a net-work of 

 capillaries ; it gives rise to numerous branches from both sides in its 

 course along the mantle margin. 



The palpal artery passes through the anterior lip of the mouth to the 

 outer side and divides into outer and inner palpal branches ; the outer 

 branch passes into the outer labial palp in a conspicuously sinuous course 

 lying in the outer lamella of the two, of which each palp is composed ; 

 the inner branch passes into the inner labial palp in a slightly undulating 

 manner lying in the inner lamella. 



The anterior aorta in its course through the visceral mass gives off 

 minute branches to the stomach, and the digestive gland ; it also gives 

 rise to a large pedal artery near the posterior end of the stomach. 



The pedal artery passes downwards and forwards through the visceral 

 mass and reaches the muscular foot at the junction of the anterior and 

 middle thirds of its length and then passes nearly to the extreme margin ; 

 it supplies branches to the intestine, rectum and the genital organs. 



The posterior aorta is a very small artery arising from the ventral 

 aspect of the posterior end of the ventricle beneath the rectum. It 

 passes along the ventral surface of the rectum between the two posterior 

 retractor muscles of the foot where it divides into 2 branches, one on 

 either side. Each branch gradually passes outwards along the posterior 

 retractor muscle and reaches the posterior surface of the posterior 



