564 Bulletin 47, United States National Museum. 



for N. nigrum, but it has possibly been partially obliterated ; the one on 

 the lower part of the peduncle is much larger. Coloration, purplish 

 brown. 



Type 5 inches in length, obtained by the Albatross from station 2553, in 

 39 48' N. latitude, 70 36' W. longitude, at a depth of 551 fathoms. In 

 a second individual from the Gulf Stream the pectoral is much more 

 developed than in the type, its length being f that of the head, and reach- 

 ing nearly to origin of ventral. The species is abundant in the Gulf 

 Stream, where many examples have been taken. (Goode & Bean.) 



(Named for Marshall McDonald, United States Fish Commissioner.) 



Nannobrachium macdonaldi, GOODE & BEAN, Oceanic Ichthyology, 94, fig. 100, 1895, Gulf Stream. 

 (Type, No. 35545.) 



262. DIAPHUS, Eigenmann &. Eigenmann. 

 Diaphiis, EIGENMANN & EIGENMANN, Proc. Cal. Ac. Sci., 2d Series, HI, 1890, 3, (tlieia). 



This genus is closely related to ^thoprora, its chief character being in 

 the fact that all or nearly all of the photophores are divided by a hori- 

 zontal cross septum of black pigment, giving them the form of the Greek 

 letter 6, theta. This septum is readily injured or destroyed in badly pre- 

 served specimens. Two or three* species known. (Aid, divided; 0of, 

 light.) 



846. DIAPHUS THETA, Eigenmann & Eigenmann. 



Head 3 to 3; depth 3 to 4; eye large, 3^ in head, 3 in length of the 

 blunt snout. D. 11 to 13; A. 9 to 12 ; scales 34. Each of the luminous 

 spots divided by a horizontal black line; 4 caudal spots; anal spots 

 5 + 5 or 6 =3 10 or 11 ; no spot on base of middle caudal rays ; 4 supra-anal 

 spots in an oblique line ; 2 or 3 posterolateral spots ; a luminous blotch 

 below eye varying more or less anteriorly ; a small detached dot behind 

 this; a photophore before eye above nostril; a flat, soft, glandular body 

 attached by one side just above base of pectoral, nearly i the size of 

 pupil ; no glandular spots on tail. Body deep, compressed, with stout- 

 ish caudal peduncle ; head short and deep, the profile convex. Scales 

 entire, those of the lateral line somewhat enlarged. Pectorals small, 

 placed low, rather short, not quite reaching ventrals. Length 2| inches. 

 Point Loma, near San Diego, to Oregon, in deep water ; the specimens! 



* Besides Diaphus theta, the character of divided photophores appears also in Diaphus engraulis 

 (Gunther) and in Diaphus cseruleus (Klunzinger). Liitken regards engraulis as a synonym of 

 cseruleus. In Diaphus cseruleus there is a luminous blotch below eye as in Diaphus theta. The body 

 in D. cseruleus is more elongate, and the dorsal ends just before first ray of anal. 



f Concerning these specimens Dr. Gilbert observes: 



" They are identical with the types of Myctophum protoculus^ and are in a state of preservation 

 sufficiently good to show the division of the luminous spots, a character not visible in the types 

 of M. protoculus. It is obvious that the spots are divided into upper and lower halves which are 

 structurally different, the narrow pigment band indicating this separation on the surface. 



"The specimens before us show great variation in the size of the Bubocular luminous blotch, 

 and indicate how little dependence can be placed on that character. In addition to the round- 

 ish supranasal blotch described by Eigenmann, the species possesses a more or less developed 

 subocular bar. In one specimen the latter is a bare line, with a minute point separated from it 

 posteriorly. In others it is wider, and in the extreme in this respect we find a bar, the width 

 of which is % the diameter of the pupil. There remains constantly separated from it the small 

 dot already referred to. A peculiar soft flattish body % as large as pupil is attached by one 

 edge to the shoulder girdle just above the insertion of the pectoral fin. It is constantly present 

 and uniform in position in all specimens seen, including the types of theta and protoculus. It 

 may be a luminous organ, though it has not strikingly the appearance of one, and its nature 

 may be considered problematical." 



