566 Records of the Indian Museum. [Vol. XXII, 



ii. Shell as a rule more than 8 mm. high, not so 



fragile with the spire normal and consisting 



of at least three whorls ; columellar fold 



twisted ... L. shanencsis. 



II. Whorls of spire transverse and increasing rapidly in 



size; suture not markedly oblique; at least four 



whorls in spire ; columellar callus very coarse and 



broad ; columellar fold coarse. 



A. .Apical whorls of spire much narrower than 'others, 



forming a distinct apical process ; penultimate 

 whorl ot shell much narrower than upper part of 

 bod3-whorl, broader than height of spire ... L. ovalis. 



B. Whorls of spire increasing in size evenly ; penulti- 



mate whorl at least nearly as broad as upper ex- 

 tremity of body-whorl, 

 i. Shell almost symmetrical bilaterall)- and its outline 

 terming a remarUably even broad ovate figure, 

 with the base of the spire more than twice 

 as broad as its height ; umbilicus imperforate L. ova/iur. 

 ii. Shell of elongate ovate form, with the spire rela- 

 tively long and narrow and the bod\-whorl 

 sub-cylindrical ; umbilicus imperforate .. L. Iiiteola. 



iii. Shell varying greatly in outline but always opaque, 

 with the suture much more impressed and 

 more oblique than in the last two species ; the 

 umb.licus, though always completelj' occlud- 

 ed by the columellar callus, usually forming a 

 narrow aperture visible on the dorsal surface L. andei-suniana. 



There is no genus amongst the Indian molluscs more liable 

 both to individual variability and to plasticity in response to en- 

 vironment than Limnaea. The two phenomena are not always 

 correlated in the same species and both differ greatly in degree in 

 different species. Probably neither is ever completely suppressed. 

 These facts make it difficult to assign specific limits to the numer- 

 ous forms, and at the same time render it probable that the 

 number of true species is small. 



Various attempts have been made to solve the taxonomic 

 difficulties involved in the study of the Indian Limnaeidae. The 

 most successful in practice was that of the late Mr. G. Nevill,' but 

 unfortunately he gave no arguments for adopting the course he 

 followed. Von Martens'^ has discussed certain species in detail and 

 has given admirable figures, but he had not seen by any means 

 all the Indian forms. We have now been able to study Limnaea 

 in relation to its environment in many parts of Peninsular India 

 and the Indo-Gangetic Plain^ on the North West Frontiers and at 

 several places in Assam and Burma, and we believe that we have 

 seen specimens of almost all the Indian forms to which specific 

 names have been given and, with the exception of the Eurasian 

 species of the Western Himalayas, have examined the natural 

 surroundings of the great majority. This has given us confidence 

 to discuss the species on broad lines, both from a geographical 

 and a purelj' taxonomic point of view. 



' Hand List Moll. Ind. Miis. I, pp. 232-234 (1878). 

 2 Condi. Mitth. I, pp. 75-80, pis. xiv, .\v (t8Si). 



