6i6 Records of the Indian Museum. [Vol. XXII, 



The mantle is very thin and without any papillae on the edge. 

 Its flaps differ from those of the genus Corbicula in having a fairly 

 broad portion of the free edge reflected inwards towards each other. 

 The siphonal and pedal orifices are formed in the same way as in 

 Corbicula by the union of the flaps of the two sides. 



The two siphons, anal and branchial, are quite separate tubu- 

 lar structures capable of a fair amount of elongation ; of the two 

 the branchial is much better developed Both siphons have 

 smooth edges for the external openings, there being no papillae 

 encircling them. Jacobsen ' describes the siphons as having 

 " filaments encircling the apertures," this seems to be a mistake as 

 none are present in S. indicum and none are shown for the Ameri- 

 can species described and figured by Gilmore;'^ Fischer^ also des- 

 cribes the orifices of the siphons in this genus as simple. 



Jacobsen's account of the gills in S. cornea is inaccurate when 

 he says that " the interior gills overlap the exterior ones," and a 

 good deal of what he says further on is not easy to follow. F. 

 I/Cidig's'* and Oscar Schmidt's' papers contain very little on the 

 structure of the gills of the European species dealt with by them. 

 I have not seen Drew's paper* on the anatomy of S. sulcatum but 

 from the summary in Gilmore's paper cited already these two 

 accounts seem to be the best ones available, Gilmore's description 

 of the attachment of the inner lamellae of the inner gills, how- 

 ever, does not appear to be accurate when he says " the inner 

 lamella of the inner gill is attached to the body," for in S. indicum, 

 as is usual in other Cyrenids, at least a portion of the inner gills (in 

 this case nearly one-fourth of the total length) projects beyond 

 the posterior limit of the body-mass. This posterior part of the 

 inner lamella is not fused with that of the corresponding part of 

 the lamella of the opposite side but is quite free. The two pairs 

 of gills dift'er in length and width. The inner pair of gills is more 

 than twice as broad as the outer throughout, while in the anterior 

 region it is still broader ; anteriorly it also extends a little further 

 than the inner pair of gills. 



In the specimens examined the marsupiuni was found to be 

 formed by the cavities of the filaments of the inner pair of gills 

 only, as was observed by Gilmore in the American species. The 

 Manipur specimens were collected during February and March, 

 1920, and it appears, therefore, from the stage of development of 

 the embryos in the brood-pouches that the breeding season of this 

 species in Manipur starts some time in January if not earlier. 



The labial palps are triangular, slightly elongate structures 

 partly covered over by the anterior portion of the inner pair of 



' Proc. Roy. Dan. Soc. Nat. Hist. Ill (18281, translated by Prime in Bull. 

 Mus. Comp. Zool. Harvard V, pp. 49-54, pi. iii (1878). 

 - Nautilus XXXI, pp. 16-31, pis. V, vi (1917). 

 ■' Man. de Concholiol., p. 1093 (1S87). 



♦ Miiller's Arch. Aiiat. Physi'ol., pp. 47-66, pi. vi, figs. 8-18 (1855). 

 ' /bid., pp. 428-439, pi. xvi (1854). 

 " Pfoc. Iowa Acad. Sci. Ill (1895). 



