50 Part I1I.—Twenty-fourth Annual Report 
paratively smooth, while any sculpture with which the earstone may be 
ornamented is more frequently found on the outer or concave side. The 
upper margin of the earstone is also the one which is likely to have the 
edge notched or crenulated, whereas the lower margin is often tolerably 
even and gently curved. 
The earstones of the Pleuronectid@ are generally more or less circular 
and sometimes nearly circular, in other cases they are broadly oval, and 
they are nearly always flat and thin. Their true position in relation to 
the head is, for this reason, and also because of the remarkable change 
that takes place in order that both eyes may be accommodated on the 
same side, not so obvious as in the case of those whose eyes retain their 
normal position. 
Secondly, a few general remarks about the size, structure, and form of 
the earstones of different fishes and their value as a means for the 
identification of species may be useful here. As already stated, it is 
many years ago since the earstones of fishes were taken up as a systematic 
study. This study was undertaken for the purpose of ascertaining if, 
failing other evidence, the species of a fish could be determined by the 
earstones alone. I soon became satisfied that, except in certain cases, 
they could not be altogether relied upon for this purpose, especially when 
dealing with young fishes whose otoliths have not yet attained the form 
and structure peculiar to the adult. But though it may frequently be 
difficult to distinguish the species of a fish where the otoliths are the only 
parts left by which it may be identified, yet they may be fairly reliable 
as a guide for ascertaining the family and also sometimes the genus to 
which the fish belongs. It is not difficult, for example, to distinguish 
the earstones of the more typical of the Gadoids, and especially of those of 
most of the genus G'adus—they are usually so massive in structure as to 
differ in this respect alone from those of almost all other groups of fishes 
with which I am familiar. Yet there are one or two species belonging 
to this family that possess earstones so different from those of the genus 
Gadus, that if it were the case that no other parts of the fishes were 
available for determining the family they belonged to, one would be 
inclined to ascribe them to some other than that of the gadidz. I have 
already referred to the family Pleuronectidee as possessing earstones more 
or less rotundate, flat and thin, and thus presenting characters by which 
they differ from most of the other teleostean fishes mentioned here. But 
though the peculiarities in shape and structure that characterise the 
earstones of fishes may not generally be reliable for the identification of 
species when unsupported by other evidence, still there are several fishes 
that possess otoliths so distinct, that by means of them alone the species 
may be determined with almost absolute certainty. In support of this 
statement I need only refer to the following species:—The earstones of 
the black goby, Gobius niger, possess characters by which they may be 
distinguished with tolerable certainty from those of other fishes. They 
are nearly flat, and of a broadly rhomboid form, as may be seen on 
pl. ii. B., figs. 19 and 20, and pl. v., fig. 6. 
The earstones of the whiting have also a form unlike that of the 
otoliths of any other fishes known to me; they are considerably elongated, 
and aze obliquely truncate at one end, while the opposite end is drawn 
out into a tapering extremity which ends in a sharp point (see figs. 30 
and 31 on pl. ii. a.), 
The hake has earstones so different in shape and so thin that when 
placed beside the massive otoliths of the cod and coal-fish, belonging to 
the same family, they suggest doubts as to whether these species are so 
closely related to one another as their position indicates, 
