FINS OP GANOIDS AND TELEOSTS. 583 



account in tlie light of an examination of a specimen of the 

 same species which I have recently had the opportunity of 

 dissecting. 



Dorsal fin. — In all essential features this fin closely resembles 

 that of Diodon hystrix. In the series of radial elements there 

 are fifteen proximal segments and seventeen distal. Of the 

 proximal segments, the first difi'ers in shape from the others, and, 

 as it takes no share in the support of the fin-rays, simply acts as 

 a buttress to the second, to the anterior margin of which it is 

 closely applied. The remaining proximal segments are expanded 

 and flattened out at their proximal extremities, where they are 

 in close contact with one another and, at the same time, wedged 

 in between the vertebral neural spines. Towards their distal 

 ends the segments contract and become nearly cylindrical, and, 

 finally, their cartilaginous distal extremities fuse indistinguish- 

 ably into an exceptionally thick, longitudinally disposed mass 

 of cartilage, which is marked by a longitudinal groove along its 

 dorsal border and traversed by a succession of deep vertical 

 grooves on each of its lateral surfaces for the passage of the 

 tendons of the fin-muscles. 



The distal segments vary considerably in size and shape. 

 The first is short, thick, and somewhat flattened laterally ; the 

 succeeding four or five rapidly elongate and become thick, 

 four-sided, tapering cartilaginous rods; those following, while 

 retaining much the same shape, gradually dimiuish in length and 

 become more slender; while the last two or three of the series 

 are irregularly shaped cartilaginous masses. All the distal 

 segments are firmly connected with one another by ligament, 

 and their rounded proximal ends fit into the longitudinal groove 

 on the dorsal margin of the proximal segments ; they are also 

 in ligamentous connexion with the proximal segments, but the 

 union is, nevertheless, of such a character that the distal seg- 

 ments and their fin-rays are capable of a considerable range of 

 ateral movement on their basal supports. 



The fin-rays agree in number with the distal radial segments. 

 Of the anterior six the first is short, but the others, rapidly 

 increasing in length, remain undivided and support the relatively 

 unyielding anterior margin of the fin. The remaining eleven 

 rays fray out, as it were, at the distal ends and, gradually 

 diminishing in length, support the flexible cutaneous fold which 

 fringes the posterior margin of the fin from its apex downwards. 



