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



The question arises whether the fish was really captured at this great depth, or 

 whether it entered the dredge during its passage through the surface strata ; and I am 

 very much inclined to think that the latter took place. We have very little positive 

 information as to the habits of these fishes, but we know that they are commonly 

 obtained near the surface in mid-ocean ; and from their structure we may infer that, 

 like all deep, compressed fishes, they are slow swimmers, and that they can with ease 

 maintain a free position in the water, without the necessity of a support, remaining as it 

 were suspended at a certain distance from the surface. This may be observed in a fish 

 of our own seas with a similarly elevated Iwdy, viz., the John Dory, in which, however, 

 a rapid undulatory movement of the soft dorsal fin is almost unceasing. The great 

 development of the luminous organs, combined with the large eyes, indicates the 

 nocturnal habits of the fish, which would induce it to descend to a greater depth 

 during daytime. Also the firm structure of the bones disproves the bathybial habits 

 of Argyropelecus. 



Sternoptyx (Herm.). 



Body much elevated and compressed, passing abruptly into a short and compressed 

 tail ; the angle made by the hind margin of the trunk and the lower edge of the tail 

 being filled up by a broad fold of the integument, of peculiar transparent aj^pearance, 

 resembling thin cartilage. This fold bears the anal fin and is supported by interhsemal 

 rays. The greater portion of the body is scaleless, and covered with a silvery pigment. 

 A series of luminous spots runs along the lower edge of the abdomen, and is separated 

 from that of the other side by a cartilaginous fold occupying the median line of the 

 abdomen ; another series runs on each side of the isthmus ; a row of three above and 

 behind the root of the ventrals, and another row of three above the vent. The luminous 

 organs on the lower part of the tail consist anteriorly of a row of four, of which the first 

 is prolonged towards the back as a narrow band, terminating about the middle of the 

 depth of the body in a globular black spot with a white centre : posteriorly in front of 

 the caudal rays there is another row of four small spots. 



Head short, compressed, deep, with extremely short snout and a wide subvertical 

 mouth. Bones of the head firm, some of them terminating in short spines, namely, the 

 angle of the pr^operculum, the postero-inferior angle of the mandible, and the symphysis 

 of the humeral bones. The margin of the upper jaw is formed by the maxillary and 

 intermaxillary, the latter being very short ; both these boucs have a sharp edge which 

 is armed with a series of very small teeth, somewhat unequal in size ; lower jaw 

 with a similar dentition ; vomer and palatine bones toothless. Eyes large, lateral. 



