THE NORTHERN RIBBON-FISH. 17 
upper extremity mto two little branches (Pl. II., Fug. 10, 7.b.). The posterior 
process of one approximates to the anterior process of the interspinous bone behind 
it, and forms with it a support for the fin ray (fr.). The stem and processes are 
hollow, the latter being cup-shaped, with an irregular sub-rectangular margin. 
Both are winged in four places in two planes, transverse and longitudinal. On each 
side of the stem, in the longitudinal plane, and a little below the fork, a broad wing 
occurs, which may be traced upwards on to the process where it becomes reduced, 
and down on to the stem where it dwindles away. Similarly, two wings occur in 
the same part of the stem, but in the transverse plane. Each forks above to go to 
the two processes, and each below runs downwards to form a ridge upon the stem. 
The supporting arms undergo very little modification except in the rudimentary 
ones near the posterior extremity (Fig. 6). Anteriorly the arms are very short, 
and consist simply of two little cups set at an angle to each other. Passing 
back they get larger and more distinct. Posteriorly they are not so strong, but the 
processes are even better developed than in the middle of the body. Anteriorly 
the arms are about the same size, but the posterior gradually get larger than the 
anterior as we follow the series backwards. Near the tail the posterior process and 
the stem are in the same line, and the anterior arm is borne as a branch. 
For the most part, the interspinous bones alternate with the neurapophyses. 
It is only near the head and the tail that the former exceed the latter. The first 
eighteen interspinous bones correspond with the first eleven or twelve vertebree— 
sometimes two and even three being enclosed between two neural spines. 
The longest interspinous bones lie near the middle of the body, and get smaller 
anteriorly and posteriorly ; near the tail, the merest traces are got. The anterior 
ones do not suffer the same reduction—the shortest being over an inch long. 
Dorsal Fin Rays.—The dorsal fin is supported by light hollow, unbranched 
rays, expanded cup-like at the bottom, and split, as in Regalecus, in the median 
vertical plane of the fish into right and left halves. This cup, along with those 
described for the interspinous bones, receives a nodule of cartilage, such as PARKER 
describes in Regalecus, but smaller (loc. cit., p. 24). 
The length of the fin rays reaches a maximum in the middle of the body and a 
minimum at each extremity. The greatest length seems to be over four inches at 
least, but the rays are so easily broken that none remain perfect. 
The Shoulder-girdle and Pectoral Fin (Pl. I1., Fig. 9). 
The shoulder-girdle of Trachypterus resembles, to a certain extent, that of 
Regalecus, but shows a still greater degree of modification in the points where both 
differ from the ordinary Teleostean type. The post-temporal is equally simple, the 
supra-clavicle and clavicle are narrower, straighter, and longer; the coracoid smaller 
and narrower, the scapula almost equally, and the brachials still more minute and 
rudimentary. 
c 
