Bibliographical Notices. 67 
innovation in uniting P. niveus with P. varius ; but I feel constrained 
to take this bold step, even at the risk of not being soon forgiven. 
I had for a long time great misgivings on the subject.’’ We greatly 
regret that his misgivings did not last longer, and can assure him 
that he was quite justified in his fears, and that his ‘ conchological 
friends” are “terribly shocked” at his merging the four shells 
named in their allied species. It is no mere individual opinion 
we express, but we believe it to be the opinion of all our leading 
British conchologists, that Mr. Jeffreys has been guilty of a most 
barbarous murder in the slaughter of these little imnocents. Are 
not the grounds on which these species are reduced to the rank of 
varieties untenable? It is to this general question that we shall 
address ourselves, because the limits of a brief review do not per- 
mit of our extending our observations to the discussion of the claims 
of the individual forms to specific rank. There has been an 
gxiom put forward, originating, if we mistake not, from Mr. Alder, 
that, ‘if two nearly allied forms live together under the same cir- 
cumstances, without showing any intermediate forms, the presump- 
tion is that they are specifically distinct.’’ This is a sound argument. 
But the converse of this by no means holds good. It is a most false 
argument, that, if two nearly‘allied forms do not occur together, this 
is to be received as proof of their specific identity. Yet this is the 
chief ground on which Mr. Jeffreys relies in his amalgamation of the 
above-named species. Pecten niveus occurs throughout the Hebrides, 
but P. varius is wholly absent from the district ; Nucula radiata is 
found in Milford Haven, but ‘‘always in separate parts of the bay. 
from P. nucleus.” Astarte elliptica has never beeu met with by the 
author ‘on the same ground” with A. sulcata; and Mactra elliptica 
is regarded as a deep-water form of M. solida. Now we are not 
prepared to deny—very far from it—the existence of races; but 
most certainly these cannot be cited as instances of this kind of 
variation. The allied species in qnestion, if we except P. niveus, are 
found constantly in the same locality, if not actually on the same 
ground, with the species with which Mr. Jeffreys would unite them ; 
and they are thus associated over a considerable portion of our own 
seas, as well as northward or southward of them. These, we repeat, 
are no instances of races, which are synonymous with local varieties. 
Had it been true that 4. elliptica, N. radiata, and M. elliptica- 
oceupied a totally different area of distribution from their allies 
A. sulcata, N. nucleus, and M. solida, then such a fact might be 
received as an argument that the allied forms were two races of one 
species. But this is not the fact. The cases before us are examples 
of nearly allied species which constantly coexist in the same limited 
area.. The fact that they do not live together upon the same ground 
and have not the same Aadits must surely be regarded as an evidence 
in favour of, rather than against, their specific rank. Another point, 
which it appears to us that Mr. Jeffreys has lost sight of in dealing 
with these species, is that a number of minor differences become in 
the aggregate equal to a single more marked character. 
In the formation of genera, we find that Crenella has been limited, 
5x 
