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



teeth imbedded in the thick lips ; maxillary with a marginal row of very small teeth. 

 Caudal fin forked, with a dense layer of small scales. Air-bladder with very thick walls,l 

 terminating in two short horns in front, pointed behind. • — I 



Bathythrissa dorsalis (PI. LVI. fig. A). 



Bathythrissa dorsalis, Giinth., loc. cit. 



Fterothrissus gissu, Hilgendorf, loc. cit.; Sitzungsb. naturf. Freunde Berlin, 1878, p. 156. 



B. 6. D. 56. A. 12. V. 9. L. lat. 112. L. transv. xV Ccec. pylor. 14. 



The general aspect of this remarkable fish is that of a much elongated Coregonus, its 

 greatest depth being one-fifth of the length of the body (without caudal). The head is 

 low, elongate, one-fourth of that length ; the large eye, the diameter of which is rather 

 more than one-fourth of the length of the head, occupies nearly the middle of its length, 

 slightly encroaching upon the upper profile. The width of the bony interorbital space is 

 much less than the diameter of the eye. Snout projecting beyond the mouth as in 

 Coregonus ; mouth laterally extending to below the anterior nostril ; the labial fold of the 

 mandible does not extend across the symphysis. Nostrils close together, separated by a 

 membrane only. The muciferous channel of the infraorbital is longitudinally divided by 

 a straight ridge ; angle of the praeoperculum somewhat produced backwards ; operculum 

 small ; sub- and inter-operculum narrow. 



Scales very regularly arranged ; lateral line straight, running along the middle of the 

 taU. 



The vent is situated far backwards, its distance from the caudal being less than the 

 length of the head. 



The dorsal fin is low, but the anterior rays are somewhat the longest ; it commences 

 above the middle of the pectoral, and terminates above the middle of the anal. Also the 

 anal rays are short, the anterior being the longest. The caudal fin is deeply forked, 

 densely covered with scales. The pectorals are more and the ventrals less than half as 

 long as the head. Ventrals inserted midway between the anal and the head. 



Upper parts brownish, shining silvery, lower parts silvery, minutely dotted with brown. 



Habitat. — Off" Inosima ; purchased from Japanese fishermen ; depth, (1) 345 fathoms. 

 One specimen, 15 inches long. 



Family AlepocbphaliD/E. 



Alepocephahis, Eisso. 



All the four or five species of this genus which have been described hitherto, are 

 bathybial. 



