50 



Appendices to Second Annual Report 



the extremity of the junction of the operculum with the suboperculum ; 

 whilst in the sprat the posterior point of the opercular covering is formed 

 by the operculum proper. The sprat's suboperculum is slightly shorter 

 and more triangular (Day, British Fish) than the herring's, and therefore 

 the posterior point of the junction of operculum and suboperculum is 

 nearer the ventral aspect than it is in the herring. 



The lower jaw in the young herring is always longer than in the sprat, 

 and this not only in fish of the same total length, but it was found to be 

 nearly always longer in examples where equality of length of head in 

 sprat and herring was taken as the standard, and where, consequently, 

 the whole length of the sprat was greater than that of the herring under 

 comparison. 



A considerable number of measurements of the diameter of the eye 

 showed that there was but a small and inconstant difference in size in 

 sprats and herring of similar length, the eye of the herring being, if 

 anything, generally the larger. The eyes in both species are about the 

 same distance from the tip of the premaxillse, and consequently the 

 sprat's lower jaw barely reaches the centre of the eye, while the herring's 

 does, but the sprat's eye is if anything slightly further from the upper 

 edge of the skull. 



The position of the fins and the serrated or smooth belly is one of the 

 oldest, as it is one of the best tests as to whether the fish under 

 examination is a true sprat or a young herring. 



In both the sprat and herring the lower edge of the belly, from the anal 

 fin forwards, is covered by a series of peculiarly-shaped scales (Plate III., 

 figs, la, 2a). These scales have a central longitudinal thickened edge or 

 'keel' and two lateral rays, one on each side, projecting upwards and 

 forwards. In the sprat this central keel is stronger than is the case in 

 the herring ; and whilst in both sprat and herring the anterior end of 

 the keel takes an elongated, pointed form (overlapped by the preceding 

 scale), its posterior termination is very different in the two fish, its end 

 in the sprat forming a sharp point, projecting backwards from between 

 the two lateral rays ; whilst in the herring the lateral rays, which are 

 much more slender than those of the sprat, run down to meet in the 

 middle line, forming an obtuse angle at the posterior end of the central 

 keel, the sharp backward projecting point found in the sprat being absent 

 or so slightly developed as to be scarcely visible. The flattened-out 

 ' wings ' of the scale are much larger in the sprat than in the young 

 herring, and the lateral rays are thicker, rather shorter, and more ossi- 

 fied than the slender rays of the young herring's keeled scales. The 

 rays of the sprat's scale do not form such an acute angle with the keel, 

 and they reach it nearer its posterior point. Their forward projecti.on in 

 the sprat is also less, and the tendency is for the posterior sharp point 

 of the scale to be slightly projected downwards. Although these ventral 

 scales of the herring are altogether weaker than those of the sprat, and 

 do not possess the sharp pointed end, they can nevertheless be felt to a 

 certain extent, more especially between the ventral fin and the anal 

 aperture. But although these serrations can there be felt in the herring, 

 they are soft and harmless compared with those of the sprat. Indeed, 

 so sharp are these scales in the sprat, that the continuous examination of 

 sprats by the test of drawing the finger along the belly soon becomes 

 impossible, owing to the laceration of the skin caused by the sharp 

 spine. 



In the number of these scales a considerable difference exists between 

 the sprat and herring. The sprat has 22 or 23 (22 in a very large pro- 

 portion of those examined) anterior to the ventral fin, and 11 to 13 (12 



