402 T. Bland on the Geographical Distribution of Mollusca. 
pothesis, “that the animals of the respective continents, however 
near their affinities may be, are in every case specifically distinct 
from each other,’”’ he observes :— 
“The question of the identity of these closely allied species 
must eventually be decided by their anatomy, but in the mean 
time we believe it to be perfectly safe to adopt this axiom, that 
consider them to be the analogues of each other, a convenient 
but indefinite mode of expression, which may be used to cover 
every degree of similitude from a general analogy to a close af- 
finity hardly admitting of distinction.”—p. 76. 
We are quite alive to the danger which exists of the abuse, by 
naturalists, of the hypothesis which Dr. Binney deprecates, but 
we must not argue against its use, from its abuse. 
Judging from the general tenor of Dr. Binney’s work, we do 
not hesitate to assert our belief, that had he lived to pursue the 
subject further, he would not only have concurred in the views 
expressed by Dr. Gould, and entertained by him in common with 
many of the most eminent men of the day, but himself have 
largely contributed to our knowledge of analogous species. _ 
imi not permit us to enter as fully into the question 
of the origin of species, as its very important connection with 
that of geographical distribution demands. 
Professor Forbes, in his before-mentioned paper in the “ Me= 
moirs of the Geological Survey of Great Britain,’ takes for 
granted, at the outset, “the existence of specific centres, 1. @; of 
certain geographical points from which the individuals of each 
species have been diffused.” He adds :— : 
“his indeed must be taken for granted if the idea of a species, 
as most naturalists hold,) involves the idea of the relationship of 
all the individuals composing it, and their consequent descent 
from a single progenitor, or from two, according as the sexes 
might be united or distinct.”—p. 336. 
Again, he writes, “My main position may. be stated in the ab- 
stract as follows, viz., the specific identity to. any extent, of the 
flora and fauna of one area with those of another, depends on 
both areas forming or having formed, part of the same speci 
centre, or on their having derived their animal and vegetable pop¥U- 
lation by transmission, through migration, over continuous OF 
closely contiguous land, aided, in the case of alpine floras, by 
transportation on floating masses of ice.”—p. 350. 
Lyell, in his Principles of Geology, refers most of the excep 
tions to the general rule, that distinct groups of species occupy 
separate regions, to “‘ disseminating causes now in operation,” and 
proposes the following hypothesis: ” ie 
_ Each species may have had its origin in a single pair, oF indi- 
vidual, where an individual was sufficient, and species may have 
; 
