TINS OF GAXOIBS AND TELEOSTS. 555 



development reference may be made to McMurrich'a description 

 of the osteology of Amiurus (1. c). 



Anal Jin. — The anal fin is also very similar to that of Platy- 

 stoma except for the greater number of radial elements and fin- 

 rays, which in the specimen examined were twenty-one and 

 twenty-two respectively. 



Cnidoglanis megastoma. 



Ill this Siluroid there are two dorsal fins, an anterior situated 

 immediately behind the head, and a long posterior which is co- 

 extensive with the caudal section of the trunk and continuous 

 posteriorly with the caudal fin. 



Anterior dorsal fin. — Tliis fin is very similar to the dorsal fin 

 of Amiurus and Platy stoma, except that there are but six radial 

 elements and seven fin-rays. The first three radial elements are 

 precisely similar to those of Vlatystoma, both in structure and in 

 their relations to the guard and defensive spines, the reduction 

 in the number of radial elements being at the expense of the 

 hinder of the series. The distal segment of the last radial element 

 supports two dermal rays. 



Posterior dorsal fin. — The posterior section of the dorsal fin is 

 supported by a series of slender fin-rays, all of which are deeply 

 cleft proximally and slightly branched dit'tally. The proximal 

 ends of the rays are pointed, and penetrate between the neural 

 spines of the subjacent vertebrae into the median fibrous septum 

 which separates the dorsal muscles of the trunk. Proximally 

 also the rays are in ligamentous connexion with one another and 

 with the extremities of the neural spines. There is no trace of 

 radial elements in any part of the fin. "With the possible excep- 

 tion of a few other Siluroids, the presence of fin-rays without 

 supporting radial elements is a condition which is unique among 

 Teleostean Fishes ; and I am inclined to regard the total suppres- 

 sion of such elements as a transitional stage in the degeneration 

 of the posterior dorsal fin to a vestigial adipose tin. 



Anal fin. — In external appearance the anal fin is extremely 

 similar to the posterior dorsal fin, but structurally the two are 

 very different. A complete series of radial elements is present, 

 in number about sixty-three or sixty-four, and, with the exception 

 of the first, all are bisegmental, consisting of slender, distally 

 expanded proximal segments and small nodular distal segments. 

 The fin-rays and their mode of support are also perfectly normal. 



