TINS OF GINOIDS AND TKLEOSTS. 541 



The segment itself, however, exhibits no indication that its 

 size is due to the union of originally distinct elements; and 

 I am inclined to think that the fact that it happens to sup])ort 

 two rays in addition to the one, viz. the third, which properly 

 belongs to it, is simply due to the concentration of certain of 

 the anterior fin-rays, which have apparently lost their radial 

 elements during the partial atrophy of a primitively more 

 extensive fin. Similar instances of this concentration of fin-rays, 

 and the support of two or more of them by a single radial 

 element, are to be noted in the last radial element of the dorsal 

 fin of Lepidosteus and in the first and last of a large number of 

 Teleosts. 



Anal Jin. — The anal fin lies immediately beneath the dorsal 

 fin, and consists of nine radial elements and thirteen fin-rays. 

 All the radial elements, including the first, are precisely similar 

 to the corresponding structures in the dorsal fin, bat the la^it, 

 as well as the first, supports three fin-rays. 



POLTPTEEII)^. 



Polypterus hicMr. 

 Dorsal fin. — The anterior section of the dorsal fin is composed 

 of fourteen * more or less distinct finlets, each of which consists 

 of a stout spine and a posterior membranous portion supported 

 by four soft multiarticulate rays which are attached by their 

 proximal extremities to the upper half of the posterior margin of 

 the spine. The more posterior finlets exhibit a tendency to fuse 

 with one another through the gradual extension backwards of 

 the membranous portion and its attachment to the basal portion 

 of the spine of the succeeding finlet. The last spine, that is the 

 fourteenth, is united by the membranous part of its finlet to the 

 first of a series of eight stout, similarly united, slightly branched 

 and multiarticulate fin-rays, which form the posterior section of 

 the dorsal fin. The latter fringe the dorsal margin of the 

 terminal portion of the tail, and are continuous behind with the 

 similarly constituted infra-caudal rays. The fourteen finlet-spines 



* The number of fiulets, and consequently also the number of radial elements, 

 is liable to individual variation (c/. Giiuther, Brit. Mus. Cat. of Fishes, vol. viii. 

 pp. 327 & 517) : hence the figures given above must be taken to apply only 

 to the particular specimen examined, which was 15 inches in length. It is 

 interesting to note that a somewhat similar individual variation has recently 

 been recorded for the jN'otacanthid Teleosteans (Goode & Bean, Proc. U. S. Nat. 

 Mus. vol. xvii. pp. 456-470). 



