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Part III. — 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 Pleuronectidae 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 Gadus — 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 gadidae. I have 

 already referred to the family Pleuronectidae 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 

 pi. ii. b., figs. 19 and 20, and pi. 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 are 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 pi. 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. 



