THE ANATOMY OF SGAPEULA. 



1139 



50. On the Anatomy of ScapJiula, Benson, with a description 

 of a new Species. By Ekendranath Ghosh, M.Sc, 

 M.D., F.Z.S., F.R.M.S., Professor of Biology, Medical 

 College, Calcutta. 



[Received June 19, 1922 : Read November 21, 1922.] 



(Test-figures 1-7.) 



The Lamellibranch genus ScapJmda, Benson is represented by 

 three species from the rivers of India and Burma. The anatomy 

 of all the known species is unknown to science, with the exception 

 of the gills of an undetermined species from Siam (Ridewood, 

 Philosophical Transactions, Ser. B, voh 195). The present paper 

 aims at describing the. characteristic soft parts of the genus, 

 based upon the animals of S. celox, Benson, and of a new species 

 from Siam. The specimens were received from the Zoological 

 Survey of India, through the kindness of Dr. N. Annandale. 



Text-figure 1. 

 7 



8 9 



Animal of S. celox, side view (left). X 10. 



The body is elongated, being two to three times as long as 

 it is deep, and deeper posteriorly than anteriorly. The median 

 dorsal margin is a third to a quarter less than the body- 

 length. The anterior adductor muscle is much smaller than the 

 posterior. Both the anterior and posterior ma.rgins slope back- 

 wards. The anterior adductor muscle is narrow and elongated 

 at its insertioia, and is placed rather close to the anterior margin. 

 The length of the area of insertion is parallel to the latter. The 

 posterior adductor muscle is large at its insertion and may be 

 oval or triangular in shape. It is placed a little distance from 

 the posterior margin. The foot is elongated and compressed 

 laterally; it presents a shallow fissure along the mid-ventral line. 

 The foot is perhaps capable of slight expansion round the fissure. 

 A minute byssus cavity is pi-esent in tine ventral fissiire towards 

 the posterior end of the foot. The byssus is not well developed, 

 being in the form of fine silky threads in the Siamese species- An 

 obtusely-pointed process is present at the postero-ventral aspect 



