
1865.] Contributions to Indian Malacology. 103 
to a single river and its feeders, as is the case, so far as is known, with 
U. olivarius, Lea. In other cases again, as in U. ce@ruleus, Lea, and 
its allies, one form is found over a considerable area, as Bengal, and in 
separate rivers, and is replaced at a distance, as in Scind and 
Western India, by forms which may either be considered as distinct 
species, or as local varieties, according to the value attached to specific 
rank. In the intermediate country of Central India, we find interme- 
diate forms. Now it is surely more philosophical to assume that we 
are only partially acquainted with the phenomena attending the means 
of distribution enjoyed by animals of low organisation, especially in 
the young state,* than to arrogate to ourselves complete knowledge of 
the subject, and to assert that no means of passage exist. If we sup- 
pose that facilities for migration exist, or have existed, with which we 
are unacquainted, all the facts above detailed are at once accounted for 
in the simplest manner, whereas on the theory that the species were 
originally created throughout the whole area, no explanation whatever 
is afforded of the limitation of that area, no cause shewn why the 
same species does not exist in other areas where the conditions are 
equally favourable for its existence, and still less is any explanation 
afforded of the gradual divergence of varieties at a distance from the 
typical form. Let it be distinctly noted that the case of mollusks 
and of other animals inhabiting fresh water is an exceptional one; in 
the vast majority of the members of the animal and vegetable king- 
doin, the phenomena are far more strongly in favour of the theory 
of specific centres. 
On another question, more especially treated in Mr. Theobald’s 
‘second paper, viz.: the impracticability of drawing a line between 
species and varieties in many cases, I entirely coincide ; indeed in the 
preceding pages will be found remarks upon the varieties of H. s¢mi- 
laris and its allies, and of H. rotatoria and its allies, similar in pur- 
pose to those of Mr. Theobald. I must, however, object to the 
practice of publishing names, whether of varieties or species, without 
any description, or with such extremely inadequate details, as in the 
case of Helix Arakanensis and H. geiton. I can only say that, 
* It should not be forgotten that the ciliated fry of the Unionide have very 
considerable power of locomotion, aud that even the adulis are amongst the 
most vagrant of bivalve shells, 
