ilo Records of the Indian Museum.. [Voi,. XIX, 



gradation can be observed. In the type-species of Acrosioma {A. 

 hiigeli) the structure is similar in every respect to that of A . variabile 

 and the shells of certain individuals of the latter are by no means 

 unlike those of the former. 



I have been able to find no trace of digitiform processes on or 

 near the edge of the mantle in either living or preserved specimens 

 of A. variabile or in preserved specimens of A. hiigeli. In both, 

 however, there is a peculiar arrangement of the pigment on the 

 inner surface of the mantle. It is distributed in alternate longi- 

 tudinal dark and pale streaks, the pale pigment in the living ani- 

 mal being of a bright yellow colour but fading to white in 

 spirit. 



Some of the largest of the freshwater Mollusca are included in 

 this genus. It is usually found in running water, but A. variabile 

 is common in ponds in Calcutta, The headquarters of the genus 

 are in Burma and the Sunda Is., but the type-species has an ap- 

 parently discontinuous range in Assam and South India, and 

 A. variabile, though mainly Assamese and Burmese, extends for 

 some distance up the Ganges. 



I am not yet quite sure as to the generic position of the Bur- 

 mese species assigned by Nevill and Preston to Pachychihis, lyca. 

 They are probably dwarf forms of Acrostoma and do not seem to 

 be closely related to the Central American species for which the 

 genus Pachychilus was originally used. 



Genus Melania, Lamarck. 



(1798 



Tiara, Mus. Bolten.) 



1799. Melania, I.amarck, Prodrotniis. 



1854. Tiara, H. and A. Adams, op. cif., p. 294. 



1874. Tiara, Brot., op. cit., p. 7. 



1884. Tiara, Nevill, op. cit., p. 278. 



1897. Melania, s.s., von Martens, op. cit., p. 66. 



1808. Neomelanien (in part), P. and F. Sarasin, op. cit., p. 38. 



1915. Tiara, s.s., Preston, op. cit., p. 10. 



The distribution of this genus is mainly insular and largely 

 Pacific. Within the limits of the Indian Empire it is found only 

 in the Nicobars and (doubtfully) in one of the Anadaman Islands. 

 I know nothing of the animal, but the shell and operculum are 

 very distinct from those of Melanoides or Acrostoma. Troschel ^ 

 and P. and F. Sarasin {op. cit.) describe and figure the radular teeth 

 of species of Melania as very like those of Melanoides, with which 

 the latter authors associate these species in their group of Neome- 

 lanias. The type-species is /i^^/z% aw^aifwZ^, I^inn. Those interested 

 in the revival of forgotten generic names may refer to Ball's* ac- 

 count of the Museum Bollenianum, reviewed in the Ann. Mag. 

 Nat. Hist. (8) XVI, p. 232 (1915) by " B.B.W. " 



' Troschel, Geb. der Schnecken. z. Bergrilndnng ein. nat. Classljication, I, 

 pi. viii (Berlin : 1856-1863). 



2 Dall, Misc. Publ. Stnitksonian Inst. No. 2360(1915). Not available to me. 



