i._)2i.j Mam pur i\I nil uses. 565 



AyU ATIC rUL.MON ATA. 

 l!v N. Annaxdale ami B. Pkashad. 



Tli(.' three families and inos1: ol' the genera of this order that 

 occur in the Oriental Region are well repre -rented in the collection, 

 namely the Limnaeidae, the Planorbidae and the Ancylidae, the 

 first by four species of Luitnaca ; the second by the unique species 

 iif Indoplanorhis and by species of (ivi'aiiliis, Sc^mcntiua, HippcHtis 

 (?) and the highly peculiar genus Can^pfoccrns : the third by three 

 species of the sirbgenus FcKiissia of Aiicvltts. 



This collection has enabled us to discuss plasticity and varia- 

 liility in the Limnaeidae^ to give particulars about the anatomy 

 of the different genera of Planorbidae and to revise the Indian 

 species of Ancylidae. Perhaps the most interesting points that 

 have become manifest in our investigatic)n are (i) the differences 

 ill environmental plasticity and individual variability shown by 

 different species of Limnaca ; (2) the honiogeniety of tlie anatomy 

 of the Indian species of the genus, contrasting with (3) the great 

 diversity of structure in the soft parts of the Planorbidae ; (4) the 

 generic status of the common Indian " Planorbis ' cxiistus and of 

 the scarce Camptoctras liiicniiim ; and (5) the precise systematic 

 position of the Indian Ancylidae. 



Family LDINAEIDAK. 

 Oenus Limnaea. lyamarck. 



Of the four species of the genus found in Manipur two are 

 widelv distributed in India {L. acuminata and L. oralis), the 

 range of one {L. aiidcysoiiiana) extends frmu south-western China 

 to Kashgar and Nepal, wdiile the third, here described as new 

 under the name L. ovalior, has been found outside the Manipur 

 X^illey only at Dimapur in the plains of Assam on the north side 

 of the Naga Hills. 



Small as is the number of species, they include so large a 

 proportion of the true Indian Liniiiacac that it will be worth while 

 to discuss here as briefly as possible the species that occur in 

 India proper, Assam and Burma, omitting those found only in the 

 Himalayas or in the districts west of the Indus. A key to the 

 species to be considered will form a suitable basis for discussion. 



Key to the species of Limnaea found in the Indo-Gangetic Plain, 

 Peninsular India, Assam and Buyma. 



I. Spirr 111 shell narrow and tightly (uilrd, wiih the sut- 

 ure Very oblique and the upper extreniily nl the 

 body-whorl not or hardly broader than the penulti- 

 mate whorl. 



A. .Apex sharpK' pointed ; shell usually lari^e or of 



moderate si/e, wuh at least 5 whorls ; eolumel- 



lar fold eoarse and strongly twisted L. aanuhiata. 



B. .\pex minutely rounded : shell small or minute ; 



columellar fold mueh less stroiiifly developed, 

 i. Shell less than 8 mm. liisli, very fragile, with only 

 two whorls in the spire, which is ver)- short ; 

 columellar fold narrow and not at all twisted .. L. niimcticn. 



