594 PEOF, T. "W. BEIDaE ON" THE MESIAL 



as is the case with the isolated dorsal and ventral finlets of 

 Scomher. In the Trachypteridae {Tiegalecus) only are the proximal 

 radial segments provided with antero-superior processes either 

 singly or in conjunction with postero-superior ones. 



In the Lophobranehii, as represented by the Syngnathidse 

 {SipJionostomd) , the radial elements of the dorsal fin are all 

 bisegmental, consisting of proximal and distal segments only. 

 The proximal segments are simple elongated ossicles, without 

 lateral longitudinal ridges or postero-superior processes, and are 

 in simple apposition by their cartilage-tipped distal extremities. 

 The distal segments agree in number with the proximal, and are 

 simple cartilaginous nodules connected with one another by 

 ligament in a longitudinal series. 



In the Plectognathi the radial elements are essentially similar 

 in the single dorsal and the anal fin of the G-ymnodontes {Diodon, 

 Tetrodon, and OrtJiagoriscus) , and in the posterior dorsal and 

 anal fins of the Sclerodermi {Balistes, Monacanthus) , but are 

 modified by fusion, and in other respects, in the anterior dorsal 

 fin of the two latter genera. In the Sclerodermi the cartilaginous 

 distal extremities of the proximal radial segments, although in 

 close apposition so as to form an even dorsal margin for articu- 

 lation with the distal segments, are nevertheless distinct ; in the 

 Gymnodontes, on the contrary, the extremities fuse into a con- 

 tinuous margin of cartilage traversed by a longitudinal groove for 

 articulation with the series of distal segments. In the Sclero- 

 dermi, and in Tetrodon among the Grymnodontes, the distal 

 segments agree in number with the proximal ; but in Diodon 

 and OrtJiagoriscus the former are the more numerous, and agree 

 numerically with the fin-rays they support. In the two last- 

 mentioned genera the distal segments, instead of being small in 

 size and cubical in shape, assume the form of elongated cartila- 

 ginous rods, a condition which exists in no other Teleosts. The 

 Grymnodontes are also peculiar among Teleosts in that the vertebral 

 extremities of the proximal radial segments are provided with 

 cartilaginous epiphyses. 



Vestigial radial elements in the form of slender rod-like 

 ossicles, or flattened lamellar bony plates, are of frequent occur- 

 rence in Teleosts, and apparently represent persistent proximal 

 segments which have lost their dermal fin-rays. Very often there 

 is a single vestigial element immediately posterior to the last ray- 

 bearing element of the dorsal fin (e. g. Holocentrum, Mesoprion, 

 Spliyrcsna), and not infrequently a more or less extensive series 



