142 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



They are among the most numerous fishes on 

 the high seas, where they live at a considerable 

 depth by day but often rise to the surface at night. 

 Only two species of the group, representing as 

 many genera {Diaphus and Myctophum), have 

 been recorded within the Gulf of Maine. But 

 each of these genera includes a considerable 

 number of species that are common along the 

 continental slope abreast of the Gulf, hence are 

 as likely to stray into the latter as are the two 

 that have actually been found there. And this 

 applies equally to various other genera of lantern- 

 fishes. 



The species of Diaphus and of Myctophum all 

 resemble one another in general appearance, in 

 having a short dorsal fin, with an adipose fin 

 behiod it; a deeply forked tail; large eyes; wide, 

 oblique mouth; and numerous luminous organs 

 along the sides; all, too, are blackishsilvery 

 in color. The members of each genus are 

 separable only by differences in the arrangement 

 of the luminous organs. Hence, positive identi- 

 fication of a given specimen calls for the services 

 of a specialist in the group. Should a lanternfish 

 be taken in the Gulf in which the arrangement of 

 luminous organs does not agree precisely with the 

 two described here, we suggest that it be sub- 

 mitted to the U. S. Fish and Wildlife Service to 

 be named. 25 



*> Parr (Bull. Bingham Oceanng. Coll., vol. 3, art. 3, 1928), and Tanlng 

 (Vidensk. Meddel., Dansk Naturhlst. Forening, vol. 86, p. 49, 1928) have 

 recently published critical synopses of the lanternfishes. 



Headlight fish Diaphus effulgens (Goode and 

 Bean) 1895 



Jordan and Evermann, 1896-1900, p. 566. 



Description. — This curious little fish is separable 

 from the lanternfish (p. 143) and from the pearlsides 

 (p. 144) at a glance, by the large and very noticeable 

 luminescent patch that covers the entire tip of its 

 snout (including the anterior margin of the orbit) 

 and that extends down over the edge of the upper 

 jaw, a structure that has no parallel in any other 

 fish regularly inhabiting the Gulf of Maine. It 

 also differs from the pearlsides in its much more 

 deeply cleft mouth, its even larger eyes, in the 

 more convex dorsal profile of its head, and in lack- 

 ing the regular horizontal row of luminescent 

 spots along each side about at the level of the 

 pectoral fin, that are conspicuous on the pearl- 

 sides. 26 



The four separate luminescent spots at the base 

 of the tail (besides the organ on its snout) separate 

 it from its close relatives of the genus Myctophum 

 (p. 143). The arrangement of the fins (all of 

 which are soft, the dorsal with about 15 rays, 

 the anal with about 16), is essentially the same 

 as in the latter, and in the pearlsides; the caudal 

 fin is more deeply forked than in the pearlsides, 

 the adipose fin proportionately shorter. 



Color. — The color has not been described. 

 Probably it is black, overlaid more or less with 



» The structures along the lateral line shown here on the Illustration of 

 the headlight fish are large scales, not luminescent organs. 



Figure 60.— Headlight fish (Diaphus effulgens), Browns Bank. From Goode and Bean. Drawing by A. H. Baldwin. 



