116 BULLETIN 189, UNITED STATES NATIONAL MUSEUM 



was taken. It is 58 mm. (49 mm. to base of caudal) long. The fol- 

 lowing proportions and enumerations are based on this specimen: 

 Head 5.4 in length; depth 10. Eye 4.4 in head; snout 4.5; interorbi- 

 tal 5.4; premaxillary 1.9; anal base 2.4; ventral (longest ray) 1.12; 

 and pectoral 1.75. D. 12; A. 9; P. 11; and V. 8. Judged from the 

 immature condition of these rather large specimens, having attained 

 a size at which several other species are known to be adult, the species 

 represented probably attains a large size. 



Range. — Colombia to Peru and the Galapagos Islands. 



Family MYCTOPHIDAE: Lanternfishes 



Body oblong to moderately elongate, more or less compressed; 

 mouth large; entire margin of upper jaw formed by the slender pre- 

 maxillaries; maxillary narrow, adhering closely to premaxillary; 

 teeth usually pointed, in bands, present on jaws, vomer and palatines, 

 and sometimes on tongue; no barbels; gill openings wide; gill mem- 

 branes separate and free from the isthmus; branchiostegals 8 to 10; 

 pseudobranchiae present; lateral line usually present; photophores 

 more or less regularly placed on lower part of body, large ones often 

 present on head and on caudal peduncle; scales present, extending 

 on cheeks and opercles; dorsal fin short, with soft rays only, near 

 midlength; adipose fin present; caudal forked; anal generally rather 

 short; ventrals and pectorals well developed. 



One genus is included in the Peruvian collections studied. The 

 family is composed of small fishes, very widely distributed in open 

 seas. Some of the species live at considerable depths, whereas others 

 live at or near the surface at least at times. 



Genus MYCTOPHUM Rafinesque, 1810 



Body fairly short, compressed; head short, compressed; snout 

 blunt; eye large; mouth large; jaws generally about equal; gill rakers 

 rather long and slender; only two photophores at base of caudal, 

 usually well separated from peduncle series; photophores along anal 

 and peduncle in two groups; scales cycloid, those in lateral line at 

 least somewhat enlarged ; dorsal fin beginning well in advance of anal, 

 though generally overlapping it posteriorly; ventral inserted under 

 or a short distance in front of dorsal, with seven or eight rays. 



Two species are included in the Peruvian collections studied. 



KEY TO THE SPECIES 



a. Caudal peduncle extremely slender, 5.25 in head; 19 photophores along 

 base of anal and ventral edge of caudal peduncle; ventral with 7 rays. 



teniculum (p. 117) 

 aa. Caudal peduncle not especially slender, 3.5 in head; 14 photophores along 

 base of anal and edge of caudal peduncle; ventral with 8 rays. 



affine (p. 118) 



