x INTRODUCTION. 
species. They may not be new, or they may not be species at all,—but they 
will be known; and any mistake which has been committed will be at once 
rectified,—any new name which has been wrongly imposed, immediately degraded 
to a Synonym. 
Accordingly I have been careful in this respect; and I have in some in- 
stances, given full descriptions, even of species which are certainly not new, but 
which I did not find described by previous authors with all the detail that was 
requisite for completely identifying them ; or, leaving out what they have noticed, 
I have added such characters as they have omitted. My main object has been 
to render all the species, whether rightly named or not, easily recognizable ; and, 
however little the science may be advanced by what is brought forward, to make 
that advance, so far as it goes, sure. 
The method of description, and the mode of computing the fin-ray formula, 
will be found conformable to the plan adopted in the “ Histoire des Poissons” of 
Cuvier and Valenciennes; a work which, in so many respects, must always 
serve as a model to labourers in this department of zoology. 
The colours, in the great majority of instances, were, fortunately, noticed by 
Mr. Darwin in the recent state. The nomenclature employed by him for the 
purpose is that of Patrick Syme; and he informs me, that a comparison was 
always made with the book in hand, previous to the exact colour in any case 
being noted. Where I have observed any markings left unnoticed by Mr. 
Darwin, I have added them myself; and, in most instances, I have given the 
general disposition of the colours as they appear in spirits, from the circumstance 
of their being often so much altered by the liquor, and liable to mislead those, 
who have only the opportunity of seeing them in preserved specimens. This is 
what Cuvier and Valenciennes have frequently done in their work ; and from 
them I have borrowed the practice. 
In a work of this nature, it has not been thought desirable to enter into any 
discussion of the principles of scientific arrangement, or to effect any change in 
systems already received ; its main object being the description of species. For 
this reason, I have taken the groups almost exactly as they stand in the ‘‘ Histoire 
des Poissons” of Cuvier and Valenciennes, or in the ‘“ Regne Animal” of the 
former: yet there is reason to believe that many parts of their system will be 
found hereafter to require some modification, especially in regard to families and 
genera which have for their distinctive character the presence or absence of 
vomerine or palatine teeth. The small value which is to be attached to such 
character is pointed out in some instances in the following work, and much 
dwelt upon. 
