108 THE VOYAGE OF H.M.S. CHALLENGEE. 



Mixonus, n. gen. 



I have long hesitated to describe the following fish under a distinct generic name. 

 The specimen is small, unique, and not in the best state of preservation, so that several 

 of the characters assigned here to the genus may have to be amended when other 

 specimens are discovered. Its pertinence to either Pteroidonus or Dicrolene seems to 

 be doubtful on account of the difi"erence in the shape of the head. 



The lower pectoral rays are free, not united by membrane with, but inserted on the 

 same base as the upper part of the fin ; they are but slightly stronger than the other 

 rays and prolonged. Body elongate, compressed, covered with small, very thin and 

 deciduous scales. Head slightly compressed, broad and flat above, depressed in front, 

 naked (with the exception of the parts between the mandibles, and, perhaps, of the 

 cheeks). Bones thin, with the muciferous system moderately developed ; only one small 

 spine above on the operculum ; pr^eoperculum without spine. Eye small. Vertical fins 

 united, but the narrow caudal projecting beyond the short dorsal and anal rays. 

 Ventrals each reduced to a filament, whicli consists of two rays firmly bound together in 

 their whole length; they are inserted behind the humeral symphysis and close together. 

 Snout broad, rounded, scarcely overlapping the lower jaw. Mouth very wide ; villiform 

 teeth in the jaws, on the vomer and palatine bones. Gill-laminae short ; gill-rakers long, 

 not veiy closely set. Pseudobranchise none. 



Mixonus laticejps (PL XXV. fig. B). 



Bathynedes latic&ps, Giinth., Ann. and Mag. Nat. Hist., vol. ii., 1878, p. 20. 



The greatest depth of the body is below the origin of the dorsal fin, and one-third of 

 the length of the trunk (including head). The distance of the vent from the snout is 

 two-thii'ds of its distance from the extremity of the spinal column. The length of the 

 head equals the remainder of the trunk. The crown of the head is remarkably convex, 

 covered with an extremely thin and transparent skin, which, perhaps, in older examples 

 is scaly. The interorbital space less convex, and equal in width to the length of the 

 suout including the eye. Eye small, above the middle of the length of the maxillary, 

 one-half of the length of the snout, and one-eighth of that of the head. Posterior 

 nostrils wide, open, in front of the eye. 



The distance of the vent from the ventrals exceeds the length of the head. Orioiu 

 of the dorsal fin above the root of the pectorals, its rays of moderate length, but longer 

 than those of the anal. Pectoral with a rather narrow base, as long as the head without 

 snout ; its rays are feeble, seventeen in number, of which the three or four lower ones 

 are a little stouter, detached, and prolonged. The ventral filaments do not reach as far 

 backwards as the pectoral. 



