13a. One Pol. PVO, and PVO^ about on same level. VOj markedly elevated. Dn present, Vn 

 absent. SAO series in straight line, or SAO;, offset slightly behind a line through SA0,-2- 

 A few posterior teeth ofjaws broad-based with hooked tips Diogenichthys 



13b. PVO, well below level of PVOj. VO series level. One Pol. Dn and Vn present. No broad- 

 based hooked teeth on jaws 14 



14a. SAO series markedly angulate Symbolophorus 



14b. SAO series straight or slightly angulate Myctophum 



15a. Caudal luminous glands undivided, large, silvery, usually deeply set into vertical sur- 

 faces of caudal peduncle. PO4 notelevated 16 



15b. Caudal luminous glands, if present, divided into platelets or scales that often appear to 

 be coalesced, not deeply set into vertical surface of caudal peduncle. PO4 elevated or 

 not 18 



16a. Lateral line very indistinct or absent. Prominent crescent of whitish tissue on posterior 

 half of iris. Photophores weakly developed, easily lost, apparently absent on one 

 species Taaningichthys 



16b. Lateral line prominent. No crescent of whitish tissue on posterior half of iris. Photo- 

 phores strongly to moderately developed 17 



17a. Large, elongate luminous gland in front of adipose fin. Four or five Pre, one or two Pre far 

 above lateral line and under dorsal procurrent caudal rays. Numerous minute secondary 

 photophores on head, body, and proximal part of caudal fin Dorsadena 



17b. No luminous gland in front of adipose fin. No Pre above lateral line. No secondary 

 photophores on body Lampadena 



18a. PO4 elevated 19 



18b. PO4 not elevated 27 



19a. First 3 VO in ascending straight line, subsequent VO on level of VOi 20 



19b. First 3 VO not in ascending straight line. VO2 and VO3 may be abruptly elevated, or the 

 VO series curved 21 



20a. Vn, Ant, and So absent. Dn present but often inconspicuous. Large supracaudal luminous 

 gland in males, much smaller infracaudal gland in females. No luminous scale on 

 PLO Lobianchia 



20b. Dn and Vn always present; So and Ant present in some species. No caudal luminous 

 glands. More or less prominent luminous scale at PLO in nearly all species Diaphus 



21a. Small luminous scales at bases of rays of dorsal and anal fins, 5 VO 22 



21b. No small luminous scales at bases of rays of dorsal and anal fins; 4 or 5 VO, the second 

 and third elevated in some genera 24 



22a. Five Pre closely spaced in continuous, nearly straight line. All upper photophores well 

 below lateral line; 5 VO, the series curved. VO2, VO3, and VO4 above level of VO, and 

 V0= Lampanyctodes 



22b. Three or four Pre, the series angulate. Upper photophores immediately above or below 

 lateral line; 5 VO, only VO2 elevated, the rest on same level 23 



23a. Three Pre. Crescent of whitish tissue on posterior half of iris. Upper photophores touch- 

 ing slightly below or above lateral line. SAO series only slightly 

 angulate Bolinichthys 



23b. Four Pre. No crescent of whitish tissue on posterior half of iris. Upper photophores 

 touching but not above lateral line. SAO series notably angulate Lepidophanes 



24a. SAO series in straight or very slightly angulate line; 3 to 4 Pre 25 



24b. SAO series markedly angulate 26 



25a. One Pol. All upper photophores several diameters below lateral line; 3 or 4 Pre, evenly 

 spaced incurve Stenobrachius 



25b. Two Pol. All upper photophores touching or very near lateral line; 4 Pre, the series 

 angulate, upper Pre widely separated from the rest Parvilux 



11 



