38 



PROCEEDINGS OF THE NATIONAL. MUSEUM 



VOL. 76 



Measurements of Diaphus chrysorhynehUrS CHlhert and Cramer 



[In per cent of the total length without caudal fin] 



Total length without caudal fin in mm - 80 75 63 



Length of head 29 31 30 



Greatest height 21 21 21 



Length of lower jaw 21 21 21 



Diameter of eyes 8.1 8.7 8.7 



Snout to D... 41 43 42 



Snout to A 61 65 63 



Snout to V 41 44 42 



The description of the supraorbital organ as " a triangular or 

 heart-shaped portion of it (the " anteorbital gland ") at the antero- 

 dorsal angle of the orbit " has proved inadequate for conveying to 

 subsequent investigators the proper conception of the morphological 

 status of the organ in question. This supraorbital organ is quite 

 distinctly, although narrowly, separated from the upper antorbital 

 by a dividing ridge running obliquely upwards and mesad in a trans- 

 verse plane at the anterior end of the snout. The subraorbital thus 

 occupies a shallow, more superior and lateral concavity of its own, 

 while the concavity of the upper antorbital is en- 

 tirely transverse and forwardly directed (compare 

 the figs. IT and 18). There is apparently no con- 

 tinuity between the luminous tissues of the upper 

 antorbital and the supraorbital organs in any of the 

 specimens, the very conspicuous dividing ridge ap- 

 pearing as a narrow, lack lustrous, black line be- 

 tween the highly lustrous, silvery tissues of the or- 

 gans themselves. These features of the circumor- 

 bital organs in D. chrysorhynchus are strongly af- 

 firmative of the opinion already previously ex- 

 pressed by the author that the so-called upper 

 antorbital of such forms as D. effulgens Goode 

 and Bean, 1895, is not homologous with the upper 

 antorbital organs of the other Myctophinae, but rather with the 

 constricted supraorbital portion of the upper antorbital in D. meto- 

 podampus^ which is again undoubtedly homologous with the supra- 

 orbital of D. chrysorhynchus. A comparison between the accom- 

 panying diagram (fig. 16) and the illustration of the circumor- 

 bital organs in D. effulgens already previously rendered (Parr, 1928, 

 fig. 30, no. 6, p. 140) makes this relationship quite obvious. The 

 author therefore no longer feels any hesitation in regarding the 

 circumorbital organs of Division IX in the key to the genus Diaphus 

 (Parr, 1928, p. 120) as developed through the differentiation of a 



Figure 17. — Fron- 

 tal VIEW OF THB 

 HEAD OF Diaphus 

 chrysorhynchus 

 Gilbert and 

 CramkRj showing 

 the antorbital 

 and supraorbital 



ORGANS 



