ig2r.] Manipur Molluscs. 605 



Preston's siliguriensis, which is a variety ot L. lima will also have 

 to be removed from the Radiatula section. 



It is not possible to decide definitely the exact position and 

 relationships of /. crispisulcatus , the only other species left in the 

 Radiaiula section, as we know nothing of its anatomy, but its 

 very characteristic sculpture alone might entitle it to a sectional 

 rank. 



The shells collected by Mr. S. L. Hora are from the .Sikmai 

 Stream on the Manipur-Burma Road. The specimens are quite 

 typical of the species but have the umbones much eroded. 



The soft parts resemble those of /. occatus. 



Genus Latnellidens, Simpson. 



1900. Lamellidens, Simpson, op. cit.. p. 854- 



1912, Lamellidens, OrCmann, Ann. Carnegie Mas. N'lH.p. 277. 



1914. Lamellidens, Simpson, oj). cit., p. 1165. 



1915. Lamellidens, Preston, op. cit., p. 174. 



1918. Lamellidens, Prashad, JRec. Ind. Mus. X\'. pp. 144, 145. 

 igig. Lamellidens, id., ib., XVI, p. 293, fig. 4. 



Simpson in the two works cited has greatly cleared up the 

 synonymy of the various Indian species, but owing to the limited 

 material at his disposal his descriptions are not quite accurate 

 in all cases. At the time of the publication of his first work 

 nothing was known about the animal of anj^ of the species and 

 the position assigned by him to this genus in his classification was 

 not correct. In his second work, though he included a refer- 

 ence to Ortmann's paper, he still stated that the soft parts 

 were not known. Preston has unfortunately created a great 

 deal of confusion as to the nomenclature of the various species 

 and varieties by indiscriminately combining many good species 

 without assigning any reasons and in other cases by describing 

 already known species as new. In mj' papers on the anatomy 

 of the genus Lamellidens , I followed Preston's nomenclature and 

 my description of the soft parts of the genus was based on speci- 

 mens which could, according to Preston's identifications, hardly 

 be separated from L. marginalis subsp. corrianus. Having now 

 carefully studied the large collection in the Indian Museum and the 

 fresh coUection from Manipur I find that the above conclusions 

 were not justified. Preston's identifications of the Indian 

 Museum collection are quite unreliable in many cases, the same 

 species having been identified differently on different occasions. 

 In this paper I do not attempt any more than to assign the 

 Manipur shells to their proper species and to add notes on the 

 distinctive characters of these forms. 



On examining fully gravid specimens of the typical L. margi- 

 nalis, it was found that the marsupium in this species is not 

 formed by the outer pair of gills only but by all the four gills. 

 In L. consobrinns and L. corrianus on the other hand only the 

 outer pair of gills is marsupial. The soft parts of all these species 

 are quite similar in other respects. It appears, therefore, that in 



