1866. | Contributions to Indian Malacology. 135 
The present list, therefore, is merely an instalment of what I hope 
may be an illustrated monograph of Indian Unionide. 
It is not my intention at present to enter at all fully into the 
question of the limitation of specific forms. I would merely point 
out, that some of the described species are certainly within the ordi- 
nary limits of variation of others described as distinct. Thus out of 
one tank in Calcutta, I have taken specimens unquestionably belong- 
ing to U. Corrianus, Lea, others which were nearer to U. lamellatus, 
Lea, and young specimens representing U. bilineatus, Lea, whilst 
other forms again appeared to appertain to U. anodontina, Lam., (or, 
at least to the species figured as such in Kister’s monograph) which 
by Lea is classed as a variety of U. marginalis, Lam. Yet all these 
forms were unquestionably identical, being united by numerous inter- 
mediate varieties, all living together in the same small pond. 
Lea’s figures in the Journal of the American Philosophical Society, 
and the Transactions of the Academy of Natural Sciences of Philadel- 
phia, are so good and characteristic, that the difficulties which might 
otherwise exist in identifying forms discriminated by such minute 
and variable characters are obviated. Benson’s species, of which only 
descriptions exist, are far more difficult to identify, and Gould’s, 
which are but briefly described, still more so. Kister’s monograph, 
in Martini and Chemnitz’s Conchylien Cabinet, contains figures of but 
few Indian and Burmese Unios, and of those, several are incorrectly 
named. 
For convenience sake, the species of Unio inhabiting India proper, 
Ceylon, Assam, and Burma will be separately enumerated. The 
species referred to Anodonta are so few that subdivision is unnecessary, 
especially as none occur in India or Ceylon. No typical form of the 
genus is known to exist in the Indian or Burmese area. 
The following works are referred to in the ensuing pages by the 
abbreviations appended in each case. 
Miili.—O. F. Miller, Historia Vermium, 1774 (not procurable in 
Calcutta). 
Chemn. Conch. Cab.— Martini and Chemnitz systematisches Conchy- 
lien Cabinet. About 1780? (not procurable in Calcutta). 
Gmel.—Caroli a Linne Systemata nature. Tom. I, Pars. VI, 1789. 
Lam,—Uamarck, Histoire des Animaux sans vertebres, Vol. VI. 1819. 
