466 Survcij of Fishing-Grounds, West Coast of Ireland, 1890-1891. 



The possession of such a series is the greatest assistance in identification, 

 since the resemblance which each specimen bears to its immediate neighbour 

 bridges over the discrepancy of the extremes. It is especially useful when, as in 

 the 2)resent instance, a species has only been known previously from the descrip- 

 tion of a particular size, since the discoverer cannot be expected to anticipate the 

 conditions in stages which he has never seen, and in attempting to do so, except 

 in the vaguest possible manner, would only be wasting his own time and that of 

 his readers. Hence, a small example of a species of which only the adult stage 

 has been described might well present such differences of proportions, and other 

 characters dependent on age or size, as to run the risk of becoming the type of a 

 new species, ultimately destined to the fate of a synonym. We certainly know, 

 thanks chiefly to Dr. Giinther's researches, that certain proportions and characters 

 vary with the size of the individual, as indeed is the case in all fishes, but it is 

 impossible to compute the relations of size to degree of development of such 

 characters with sufficient accuracy to eliminate all risk of confusing nearly 

 allied species. Such must be our excuse for a somewhat tedious discussion of the 

 condition of each example of the series. 



In the largest example, X, the eye is contained about three times in the length 

 of the head, while in the smallest it occupies only about two-fifths of that 

 dimension. In this case the length of the eye is taken to be the distance between 

 the most anterior and the most posterior point in its circumference. Except in 

 the largest example it is not circular, but longer than high, its greatest actual 

 length being in an oblique direction, parallel to the infra-orbital ridge, while its 

 least diameter is vertical to the course of that structure. The Table of dimen- 

 sions shows sufficiently that this elongation is a feature which tends to disappear 

 with the growth of the individual, and we need only add that the flattening of 

 the inferior margin of the eye in the specimens forming the middle of the series 

 replaces a slight concavity in the smallest of all, which seems to indicate a very 

 late persistence of the choroidal notch in this species. 



That the alteration in the proportion borne by the antero-posterior diameter 

 of the eye to the length of the head is gradual, and extending, jjari passu, with the 

 growth of the fish, is shown very clearly when the first-named dimension is 

 converted into a decimal of the other, the result being, in X -33, in A -35, inB '39 

 in C 41, and in D '42. The growth of the snout, as compared with that of the 

 eye, appears to be more commensurate, the former maintaining a dimension 

 varying from three- to four-fifths of the latter throughout the series. It is 

 certainly largest in the largest specimen, but the pro^jortionate diminution shown 

 by the second specimen is not regularly maintained by the remainder, the figures 

 of the snout in terms of the eye being as follows : X -78, A -61, B -65, C 59, D '62. 

 The length of the snout in X, therefore, is probably partly illustrative of 

 individual variation, and not solely of developmental change. 



