of the Fishery Board for Scotland. 



'271 



mm., and the others from f to 1 mm. in length. The 19th or ventral ray 

 is generally longer than the most dorsal by 3 or 4 mm. in the adult herring. 

 The intermediate rays become shorter consecutively from these outer rays 

 to the centre of fin, and they are jointed like the others, but at about one- 

 third from their roots they split longitudinally and laterally into numerous 

 (commonly five or more) filaments, which, however, also are transversely 

 jointed. All of these rays, including the accessories, consist of two lateral 

 portions (as if split vertically from end to end) closely approximated 

 throughout their whole length, and they each, with the exception of the 

 central pair (10th and 11th from dorsal surface), arise proximally from 

 a pair of longer bony unjointed basal pieces. These bases have the form 

 of short (3 to 7 mm.) rods of less diameter than the rays, widest where 

 they articulate with the jointed rays, and sharply pointed at their proximal 

 ends, which overlap the bones of the tail (haemapophyses or hypurals). 

 As a consequence of this external overlapping of the hypural bones each 

 limb of these basal bones is separated from the other — the left from the 

 right by the thickness of the hypural bone which supports them. The 

 pair of rays (10th and 11th from dorsal surface) forming the centre of 

 caudal fin differ curiously in the form of their basal support, in so far as, 

 instead of being short, sharp-pointed, rod-shaped bones, they take the form 

 of much more elongated, thin, flat laminae. The base of the most dorsal 

 ray (1st) is supported by the most posterior short (dorsal) hypural, and is 

 ventral therefore to the urostyle or 61st vertebra. Eays 2, 3, 4, aud 5 

 are supported principally on the haemapophyses (? 60th) immediately dorsal 

 to the upper wedge-shaped hypural, which latter carries the 6th to 1 0th 

 rays inclusive. The 11th is fixed to the narrower central diagonal bone, 

 while the large ventral wedge-shaped hypural carries the 12th to 16th, 

 the 57th haemal spine the 17th, and the 56th the 18th and 19th ray 

 bases. 



The dorsal fin is of the usual construction, consisting of a series of 

 paired and transversely jointed rays, a single unpaired series of inter- 

 spinals bones acting as supports to the rays, and a series of median 

 cartilaginous nodules forming an articulating joint between these two. 

 Generally, the interspinous bones may be described as each consisting 

 of a narrow, rod-like central portion, having a sharp-pointed ventral 

 termination, and a thickened dorsal articular end. This central rod is for 

 the upper half or third of its length expanded antero-posteriorly into a 

 thin bony lamina on each side of the central stem, the posterior being the 

 larger. But it is also expanded in a larger degree laterally into a similar 

 pair of laminae or wings. In the first interspinous bone the anterior lamina 

 is much enlarged; it is as long as, and for most part of its length, is 

 separated from the main stem. The anterior and posterior wings of the 

 interspinous bones diminish both in projection and in length, going back- 

 wards, having almost disappeared on the 8th bone, and beyond the 12th 

 they are in this respect simple rod-shaped bones. The upper end of the 

 interspinous bones is bent somewhat backwards to form a kind of neck 

 slightly hollowed on its upper (anterior) surface, and each slightly over- 

 laps the one posterior to it. The posterior end of this neck is also some- 

 what cup-shaped, and the hollow formed by this end of one interspinous, 

 and the upper surface of the neck of the succeeding one forms an articular 

 hollow for the ball-shaped cartilage, which fits between the nodular later- 

 ally separated bases of the otherwise closely approximated fin rays. The 

 usual number of rays readily visible externally is 17 or 18, but the actual 

 common number is 19, the first being so small as to be partially hidden 

 by the scales. The fourth ray is the longest, and from it to the last they 

 consecutively shorten, the last being from one-third to one-half the length 

 2 M . 



