DAVIDSON — SCOTTISH CARBONIFEROUS BRACIIIOrODA. 
237 
smaller,* but not the less interesting on that account, and are in 
many instances far more perfectly preserved than any similar species 
hitherto noticed from other counti'ies, so that we have been enabled 
in several instances to complete the descriptions of the characters 
both internal and external, which were but imperfectly made out in 
cm- larger work. In a very interesting paper by Mr. McAndrews on 
the comparative size of marine mollusca, it is clearly proved that 
"although the size attained by mollusca may be influenced by various 
conditions in different localities, as a general rvile each species attains 
its greatest size, as well as its greatest number in the latitude best 
suited to its development." Much has, however, to be learned 
relative to the habitats and distribution of the British Carboniferous 
species, and correct lists of those pecidiar.to each horizon, zone, or 
stage, have still to be drawn up, as well as those that partake of 
a larger or more restricted vertical range ; and indeed, when prepar- 
ing my monograph for the Palseontographical Society, I found that 
the information I could obtain upon this very important subject was 
so scanty, and often so unsatisfactory and contradictory, that I was 
obliged to confine myself almost entirely to the working out of the 
species, which had themselves been thrown into much confusion, on 
account of the multitude of erroneous identifications or mis-naming 
prevalent in almost every British public and private collection, whde 
the nomenclature was likewise most heavily burdened with a vast 
number of synonomous and useless denominations. It could not, 
therefore, be expected in most instances that local enquirers could 
furnish that correct information relative to the distribution of the 
species in their particular districts until they had become familiar 
vrith the characters of the species themselves ; it would have to a 
certain extent been just as if we were to expect that a person could 
read fluently who was but very imperfectly acquainted with the 
name and shape of his letters ; but it is to be hoped that before long 
that important information will be forthcoming, and which no one 
could furnish or work out so well as those who reside in the localities 
where the fossils are found. The difficulty and perplexity I so often 
experience in the identification of specimens and species should deter 
many who may be even less experienced than myself from too hastily 
supposing that a shell which may not be familiar to their eye is 
really new ; for in order to ascertain whether a species is in reality 
so, a very considerable amount of research is required, a research 
many cannot undertake, from the want of books or means of com- 
parison. I would, therefore, urgently impress upon the minds of 
youiag palaaontologists the very great importance of caution, and not 
too hastily or highly consider as new what they might not be 
acqu.ainted with, otherwise the science will become so burdened with 
synon^Tns and useless denominations that it will deter many from 
* Conditions arising from foorl and climate no doiibt modify form and size, and 
modifications of form not amounting to malformation might arise from diseased 
condition. 
