6o8 Records of the Indian Musenui. [Vol. XXH, 



The animal differs from that of L. corrianus described in the 

 paper cited in the following characters : — The inner pair of gills is 

 broader than the outer throughout its length. Both pairs of gills 

 are marsupial and when fully charged with glochidia are of a dull 

 brownish colour. The palpi are comparatively larger and elliptic 

 in outline. The foot is better developed, being a powerful bur- 

 rowing organ in this species. The branchial aperture is about 

 one and a half times the size of the anal and has the papillae 

 along its border more numerous and much larger. 



Half a dozen specimens of this species were collected by Mr. 

 S. I/. Hora in a small rapid-running stream at Mara Khong at 

 a distance of about six miles from Imphal on the Bishenpur Road. 

 The shells of these specimens are quite typical of the species in 

 shape but are rather thin. 



Lamellidens consobrinus (Lea). 



1911. Lamellidens consobrinus, Ortmann, iVantilns XXI\', p. lo(), pi. 



vii, fig. 4. 

 1914. Lamellidens consobrinus (in part), Simpson, op. cit.. pp. 1171, 



1 172. 

 191^. Lamellidens mavginalis subsp. consobrina. Preston, op. cit., p. 



180. 



Preston considers L. consobrinus to be a subspecies of L. 

 marginalis. After a careful comparison of large series of the two 

 species I do not consider that this conclusion is justified. Preston 

 was probably led to it by mixing up specimens of the two species 

 while identifying the Indian Museum collection. Simpson in- 

 cludes L. tnainwaringi (Nevill MS.), Preston, as a synonym of L. 

 consobrinus. Unfortunately Preston's figures of the hinge of this 

 species are very poor and his description of the shell also lacks 

 precision in some important details. It may be noted briefly here 

 that L. rnainwaringi is a distinct species, not at all allied to Z.. 

 consobrinus, its nearest relation amongst the Indian forms being 

 L. corrianus. 



The shell in this species is rhomboidal, rather solid, with 

 the beaks more inflated and elevated than in L. marginalis. The 

 dorsal slope is curved and obliquely truncate. The hinge (fig. 

 29 B) is very different from that of L. marginalis. In the right 

 valve there are two widely separated pseudo-cardinals lying one 

 below the other, of these the lower is much larger, thicker and 

 better developed than the upper. The left valve has two some- 

 what ragged pseudo-cardinals more or less in the same line ; the an- 

 terior of the two is very much larger and better developed. The 

 laterals are distinctly arched, there being a single well developed 

 and the rudiment of a second in the right and two fulh' developed 

 ones in the left valve. 



In a single male specimen in spirit the animal conforms to 

 Ortmann's description. 



The species is represented in the Manipur collection by a 

 single specimen collected in the Sikmai Stream about six miles 



