1140 DR. E. GHOSH ON THE 



of the foot. The anterior retractor pedis muscle is narrow and 

 elongated, and consists of two heads of insertion into the valve. 

 The posterior retractor pedis muscle is narrow, and elongated at 

 its insertion into the valves just in front of the posterior adductor 

 muscle. It extends diagonally from the posterior end of the 

 foot. 



The visceral mass is greatly widened out laterally into a some- 

 what conical hump with an oblique ridge on the surface. The 

 gills are elongated, tapering posteriorly, and are about half the 

 length of the body and thrice as long as broad. The gill-axis is 

 slender, rod-like, and is placed more horizontally than diagonally 

 and ends in a small free posterior portion. The gill-filaments are 

 placed obliquely to the gill-axis, and the reflected filaments are 

 free dorsally. The labial palps are elongated, semilunar in shape, 

 and are placed at a.n obtuse angle with the gill-axis. They are 

 one-third to one-fourth the length of the body, and twice as long 

 as broad. The oesophagus is curved, with the concavity directed 

 backwards. The stomach is greatly elongated. The caecum of 



Text-figure 2. 

 s 



Animal of S. celox, longitudinal section. 



the crystalline style is small, narrow, and is fused with the 

 beginning of the intestine, the latter being placed on the right 

 side of the caecum. The intestine consists of a short anterior and 

 a long posterior limb, and is placed towards the right side of 

 the body. The rectum is placed dorsally to the heart, and ends 

 in a small free portion projecting downwards and backwards 

 from the posterior surface of the posterior adductor muscle. 

 The pericardium is divided into two lateral portions. The two 

 ventricles are widely separated from each other by a narrow 

 tube, which giA^es rise to anterior and posterior aortse. The 

 aui'icles are comparatively large ; they do not communicate with 

 each other. The digestive glands are extensive. The genital 

 organs surround the lower portion of the oesophagus and occupy 

 the ventral region of the visceral mass. Osphvadia and Thiele's 

 abdominal sense-organs are both absent. 



Structure of the Gills of S. celox. — The gill-filaments are 

 flattened antero-posteriorly as usual. There are no interlamellar 

 extensions (described in Area pexata by Kellogg (Bull, U.S. Fish 



