MOLLUSCA OF INDIA. 173 
shells which, when estivating, will not bear a journey of several 
months without injury, provided damp or excessive cold be 
avoided. 
‘“'That the introduction of a single pair of shells is ample for the 
diffusion of the species has been proved in Calcutta in the case of 
Achatina fulica. The facts are well known, but will bear repeating. 
About twenty-five years ago, 1843, two specimens were brought 
from Mauritius, and placed in a garden. Now the species abounds 
almost everywhere throughout an area of at least five miles in 
length*. In many places several hundreds might be collected. 
Ten years ago, to my own knowledge, the shell was quite unknown 
in the Botanical Gardens on the opposite bank of the Hoogly. The 
other day I saw it living there in abundance. Of course, in a large 
city like Calcutta, where plants are constantly transferred from one 
garden to another at a distance, great facilities for dispersion exist ; 
but the numbers, all unquestionably derived from a single pair in 
the course of so short a time, are nevertheless astonishing. I have 
very little doubt that one impregnated female would suffice equally 
well to introduce a species. 
‘“ Another fact in favour of Diplommatina huttoni and Ennea 
bicolor having been introduced into the West Indies by man is, that 
both are very small shells, precisely such as would most easily 
escape notice and be transported with plants. No shell is more 
likely than the Hnnea to have been thus carried into foreign coun- 
tries. The case of the Diplommatina is certainly far more difficult, 
but still it appears to me to present fewer difficulties than the theory 
of migration. Is there a botanical garden in Trinidad ? 
“If the Diplommatina has not been transported artificially, I 
should be almost inclined to suspect that the Trinidad species is not 
really identical with that inhabiting the Western Himalayas, but 
that two forms, closely resembling each other, have originated 
separately at the extreme limits of the area occupied by the genus. 
“With regard to the Ennea, I have very little doubt of its 
having been transported. Many of the cultivated plants of the 
West Indies must have been introduced by the Spaniards and 
Portuguese, some of them, in all probability, direct from India; and 
the date of the introduction may thus have been sufficiently distant 
to allow of a considerable amount of dispersion amongst the various 
islands.” 
DIPLOMMATINA OCCIDENTALIS. (Plate XLV. figs. 8, 8a, 8 0.) 
Locality. Island of Trinidad, West Indies (ex coll. Sir Rawson 
Rawson). 
Shell sinistral, elongately turreted, scarcely sinuate; sculpture 
somewhat distant well marked costulation; colour white; spire 
rather attenuate, apex blunt; suture deep ; whorls 6, sides tumid, 
the last small, the penultimate much the broadest, those above be- 
* [In 1877 I found it abundant in the gardens at Barrackpur, which is 15 
miles north of Calcutta.—H. H. G.-A.] 
