266 THE VOYAGE OF H.M.S. CHALLENGER. 



Nostrils, two minute openings in front of the eyes ; gill-openings very small, close 

 together at the lower surface of the body, immediately in front of the base of the pectoral 

 but at some distance from the angle of the lower jaw (fig. d"). 



Vent midway between the angle of the lower jaw and the extremity of the tail ; 

 the vertical fin is well developed, but does not surround the extremity of the tail, 

 showing a distinct break between the neural and haemal portions. The dorsal fin 

 commences opposite to the vent and is composed of numerous closely set delicate but 

 very distinct rays. The rays are longest on the narrow portion of the tail, but rapidly 

 decrease in length backwards. The anal is entirely similar to the dorsal as regards 

 structure and extent. Pectoral well developed, composed of about twelve r.ays, its 

 distance fi'om the eye being two-fifths of that from the vent. 



Lateral line inconspicuous, running along the middle of the tail. 



Coloration uniform black. 



This form is extremely interesting, inasmuch as it is still nearer to the 

 Leptoccphalid condition than NcmicJithys infans. In fact, I had to consider the 

 possibility of its being a less advanced stage of development of that species ; however, 

 the minute size of the eye disposes of the idea of genetic affinity. Possibly .some of 

 the long forms of Leptocephalus are the ofispring of this and the preceding genus. 



PLECTOGNATHI. 



The fishes of this order are littoral and a few only pelagic forms ; none show in 

 any part of their organisation special adaptation for a bathybial existence. All are bad 

 swimmers. It is therefore not improbable that of the following two species, at least 

 the Monacanthus was caught near to the surface. 



Triacanthodes, Blkr. 

 One species only is known. 

 Triacanthodes anomalus, Schleg. 



Triacanthodes anomalus, Giiuth., Report on the Shore Fishes, Zool. Chall. Exp., pt. vi. p. 50. 

 This species was hitherto known from Japan only. Specimens were obtained at Ki 

 Island, Station 192, where the trawl brought up a great number of new and interesting 

 forms from a depth of 140 fathoms. 



Monacanthus, Cuv. 



None of the numerous species of this genus, which is spread all over the tropical 

 and subtropical seas, have ever been recorded from deep water, with the exception of 

 the following. 



