58 Records of the Indian Museum. [Vol. XIX, 



Viscero-parietal ganglia placed beneath the bifurcation of the 

 retractor pedis posterior muscle. 



The general conformation of the body shows that the present 

 animal is considerably abbreviated antero-posteriorly in comparison 

 with that of the species of Solen. The process of elongation has 

 mainly affected the posterior region of the body behind the 

 posterior adductor muscle and a small anterior region including 

 the anterior adductor muscle. The animal is evidently more 

 primitive than the species of Solen. It is quite suggestive that the 

 type of bod}'^ in Solen might have passed in evolution through 

 a stage more or less resembling the present genus in descending 

 from a still more abbreviated type of ancestor. 



Type-specimen : No. M. ^^-J^ z.s.i. {Ind. Mus.). 



Further Notes on the Anatomy of N. aquae-dulcioris, 

 sp. nov. 



Gills. The gills are plicate and heterorhabdic. The principal 

 filament is somewhat flattened laterally and is slightly different 

 from the ordinar}^ filaments. The interlamellar septa extending 

 between the principal filaments are very short bringing the lamellar 

 closer to each other. The plicae themselves are also connected 

 with one another antero-posteriorly by interplicar tissues. 



The oesophagus is nearly horizontal with a slight curve 

 having its convexity directed upwards. The wide oesophageal 

 stomach is separated from the cardiac stomach, extending beyond 

 the former in front by a thick prominent horizontal fold. The 

 pyloric stomach does not extend beyond the coecum of the 

 crystalline style posteriorly. The central stomach is triangular in 

 shape and is separated from the cardiac and pjdoric chambers by a 

 ridge continuous with that in front. 



The shell was described and jBgured in the paper cited above. 



Gen. Ensis, Schumacher. 



1782-93. Solen (pars), I.inne, Syst. Nat. ed XIII, edited by Gmelin. 

 1817. Ensis, Schumacher, Essai d'tin. Nov. Syst. des Habit, des vers 



Testace, pp. 47, 143, pi. xiv, fig. i. 

 1840. Ensatella, Swainson, Ti'. Malac.p. 365. 

 1858. Ensis, Schumacher in Adams, Geti. Recent Mollusca, II, p. 342 ; 



III, pi. xcii, figs. 2, 2a, 2b. 

 1887. Ensis, Schumacher in Fischer, Man. Condi., p. iiio. 

 1889. Solen (pars), Clessin in Martini and Chemnitz, Conch -Cab., pp. U), 



14, pi. 



The genus has been studied by Bloomer (5) who described the 

 anatomy of Ensis ensis with full details and later on compared it 

 with several other species (11, 12, 13). Drew (25) briefi}^ noticed 

 the animal of E. directus. He figured the siphon and the ventral 

 aspect of the animal and gave a schematic transverse section of the 

 body showing the attachments of the gills not fully dealt with by 

 Bloomer. The following diagnosis is drawn from the researches of 

 Bloomer and Drew : — 



Animal. Body narrow and greatly elongated. Pedal aperture 

 either confined to the anterior margin, or extending posteriorly 



