Luminous scale at PLO about one and one-half to one and three-fourths the size of pupil, 



the tissue in intermittent, rather horizontal lines D. lutkeni 



13a. Dn and Vn both very small, inconspicuous; Vn at anteroventral margin of orbit. PLO 

 near lateral line. AOa, not or but slightly elevated; last AOa often slightly elevated. SAO 

 distinctly angulate; SAO 1.2 interspace half or less that of SAOj..'). Luminous scale at PLO 



about size of pupil, the tissue in more or less vertical lines D. dumerili 



13b. Dn and Vn small but conspicuous, Vn somewhat the larger, more or less rounded, occa- 

 sionally protruding into orbital rim, a little before vertical from hind margin of orbit. ...14 

 14a. Vn rounded or horizontally elliptical. AOai seldom elevated by more than half its diame- 

 ter above level of AOa^. PLO nearer pectoral origin than to lateral line; VLO midway or 

 lower between pelvic origin and lateral line. SAOs and Pol two to four diameters below 

 lateral line; SAO interspaces nearly equal. No luminous scales at any photophore other 

 than PLO, this scale three to four times larger than PLO, the tissue in wavy, roughly 



vertical lines D. tennophilus 



14b. Vn triangular. First AOa elevated to about level of SAO2 15 



15a. Small mounds of pigmented tissue protruding into ventral margin of orbit anterior to Vn. 

 Luminous scales adjacent to PLO, VLO, SAO:i, Pol, and Prc4. Total gill rakers 24-25 



(22-26) D.trachops 



15b. No small mounds of pigmented tissue anterior to Vn. A luminous scale present only at 



PLO. Total gill rakers 22 (21-23) D. similis 



16a. One or more of the last few AOp elevated, the last usually the highest. PLO and VLO 

 much nearer lateral line than to pectoral and pelvic bases. Pre interspaces increasingly 

 wider. Luminous scale at PLO about the size of pupil, the tissue in short, somewhat 



vertical lines D. regani 



16b. Last few AOp photophoreson same level asothers 17 



17a. Total gill rakers 13-14 (4 + 1 + 9 (8) ). PLO below level of VLO and slightly nearer 

 pectoral base than to lateral line; VLO slightly nearer lateral line than to pelvic 

 base. SAO3 well behind a line through the almost vertically placed SAOi.^- Luminous 

 scale at PLO small, 0.50 to 0.75 in pupil, the tissue in wavy or convoluted lines directed 



posteriorly D. problematic us 



17b. Total gill rakers 16 or more 18 



18a. SAO., and Pol two or more of their diameters below lateral line 19 



18b. SAOii and Pol ator very near lateral line 20 



19a. VO:! always below a line through PLO, VLO, and SAO2. SAOi on same level as last 2 VO. 

 Vn of males not extending up behind Dn and displacing it forward. Luminous scales at 

 PLO roughly ovoid horizontally, slightly larger than pupil, the tissue in long, nearly 



vertical lines D.jenseni 



19b. VO., on a line through PLO, VLO, SAO,, and AOa, (AOa, very rarely not elevated). SAO, 

 its diameter above level of last 2 VO. Vn of males with an occasionally isolated lobe 

 extending up behind Dn and displacing it forward; this lobe of Vn then resembles an Ant. 

 Vn of females often not quite contiguous with Dn. Luminous scale at PLO as large as, 



often slightly larger than, pupil, the tissue in long, nearly vertical lines D. pacificus 



20a. Posterodorsal margin of operculum strongly lobed, recurved, weakly serrate in adults. 

 Dn of both sexes large, half or more the vertical diameter of orbit. Body photophores 

 notably small. Head deep, 80-85'7f of its length. Luminous scale at PLO slightly larger 



than pupil, the tissue convoluted D. lucidus 



20b. Posterodorsal margin of operculum not strongly lobed 21 



21a. First 3 Pre closely and rather evenly spaced, the fourth widely separated 22 



21b. All Pre separated by two or more diameters, the spacing often becoming progressively 



wider 23 



22a. PLO nearer pectoral base than to lateral line; VLO usually nearer lateral line than to 

 pelvic base, but sometimes midway between. SAO2 and AOa, well below a line through 

 PLO and VLO. Dn expanded to over nasal apparatus, particularly in males. Luminous 



100 



