﻿COSMOPTYCHIUS STRIATUS. 



45 



extreme point of the tail, and l|th inch in that represented in fig. 2, whose total length 

 is 10^ inches. The dorsal and anal are large, triangular, high and acuminate in front, 

 somewhat concavely cut out posteriorly ; the caudal is very powerful, deeply cleft, and 

 inequilobate. The fin-rays are slender for the size of the fish ; their joints are delicately 

 striated (PI. Ill, fig. 8), and in the front part of the fins are considerably longer than 

 broad ; more posteriorly, however, they gradually become shorter so as to be at last 

 nearly square. Some difference in this respect is exhibited by one of Agassiz's type 

 specimens — the small one figured in the 'Poissons Possiles,' Atlas, vol. 2, tab. 4 b, fig. 3, 

 and in which the ganoid surfaces of the joints of the fin-rays are proportionally longer 

 than in the larger specimens usually met with, including those figured in the present 

 work. It may be a question as to whether we have here to deal with a distinct species, 

 unless this circumstance be attributable to difference in age ; meanwhile I am disposed 

 to wait for further evidence before adding a new specific name to the list. The number 

 of rays in the fins cannot be determined with absolute certainty ; as far as I can ascertain, 

 there are at least 42 in the dorsal and anal, and 45 in the ventral ; those of the caudal 

 are very numerous and uncountable. The principal rays of the fins begin to dichotomise 

 towards their terminations ; more posteriorly, and in the case of the caudal, all along the 

 upper lobe, the process commences earlier, viz. about the middle of their length. 



The scales of the body are remarkable for their large size on the flanks of the fish, 

 where they are higher than broad, and in the specimen represented in PI. Ill, fig, 2, 

 measure ^-ths inch in height by ^-th in breadth ; they become rapidly smaller and more 

 equilateral towards the back, belly, and tail ; on the caudal region and along the margins 

 of the fins their diminution in size is very marked. Proceeding backwards to the caudal 

 body-prolongation, we find, indeed, an immense contrast between the small size of the 

 acutely lozenge-shaped scales in this region and the large dimensions of those on the 

 flank. In one of these scales, opposite the middle of the origin of the lower lobe of the 

 caudal fin, in a specimen of about the same dimensions as that last referred to, the long 

 diagonal measures only ^oth, the short one -jVth inch ; further on towards the tip of the 

 upper lobe (PI. Ill, fig. 1) they become very minute. The caudal body-prolongation is also 

 remarkably stout and strong, and the small size of its scales causes it to display many 

 rows of them. In the specimen represented in fig. 2 several specially large scales are 

 seen in front of the origin of the dorsal fin. The upper margin of each of the flank 

 scales (PI. Ill, figs. 5, 6) is remarkably concavely cut out, the concavity of the contour 

 assuming almost the appearance of a notch ; the articular spine is moderate, the keel on 

 the under surface obsolete in the scales of the front part of the fish, and only slightly 

 marked in those situated more posteriorly. The overlapped marginal area is very narrow ; 

 the exposed surface is exquisitely sculptured with an arrangement of fine, sharply defined, 

 sub-parallel ridges, which pass obliquely or diagonally downwards and backwards across 

 the scale, sometimes anastomosing, sometimes branching or increasing by intercalation. 

 The enlarged representation of scales given by Agassiz (Atlas ' Poiss. Foss./ vol. 2, tab. 4 b, 



