666 BULLETIN (IF THE UNITED STATES FISH COMMISSION. 



acteristic of H. (ui.1r:vu.s; a conspicuouK lilaok spot at base of each anal ray; dorsal rays not marked; 

 posterior edge of occipital canal jet-black (as in H. antririm); a transverse black line on anterior edge of 

 snout; lower side n( head, opercle, breast, and belly black, this color extending a little beyond origin 

 of anal fin. As in //. imli-.rtis, the gular mendjrane has a black median streak, from which diverge 

 forward and outward a munber of tine parallel black lines. A silvery streak along each side of isthmus 

 extending liackward ami surroumling uuter portion of ventral base, cro.ssed with very fine parallel hair 

 lines of black, which can be made out only by the aid of a lens; the.se lines are as numerous and as 

 line as the scale stria-; lips and dentary portions of jaws lilack; roof of mouth shining plumbeous- 

 branchial region largely dusky; a blackisli patch in front of tongue; lining of gill-cavity largely dusky. 

 Specimens were taken as the following stations: Nos. 3920, off the south coast of Oahu, 265 to 280 

 fathoms; 3986, off Kauai, 55 to 362 fathoms; 4122, off the soutliwest c<iast of Oahu, 192 to 352 fathoms. 



Hymenocephalus aterrimus, new species. Plate 93. 



Ty(ie, 127 nun. lung, from station .3989, vicinity of Kauai Island, depth 3S5 to .'lOO fathoms; type, 

 No. 51649, U. S. Nat. INIu.^. 



This species is jet-black, and m.-curs at a greater depth than //. aittncuif or //, sirlalubix. Its range 

 is ajiparently between 400 and 500 fathoms, where it is found in corapjan}' with Mucrom-us gihher 

 and Trachoniiriix snilipellin. It is closely related to the other Hawaiian species of the genus, and to 

 H. italici.is. In additiuu to the piapery cranial crests and the wiile mucous canals bridged over with 

 delicate niemliranc, the wide terminal mouth, the weak dentition and the smooth dorsal spine, the 

 species has thin caducous scales, the peculiar striation on side of throat and region above base of 

 pectoral fin, and the 2 minute lens-like bodies in the median line of the ventral surface. 



The depth of the body varies widely with the distention of the abdomen, and also with the curvature 

 of the back, the base of the dorsal fin sometimes forming a greater prominence than in the type. In 

 the latter, the depth at origin of dorsal tin is contained 1.5 times in the length of the head. D. ii, 9; 

 V. 13 (usually 14); V. 13 (sometimes 14); 3 rows of scales between position of lateral line and middle 

 of base of first dorsal. 



Head very large, compressed, with a \ery heavy bluntly-rounded snout, which scarcely protrudes 

 beyond premaxillaries; mouth terminal, with the premaxillaries anteriorly wholly below orbit; cleft 

 oblique; maxillary reaching slightly beyond vertical from posterior margin of orbit, its length 1.85 in 

 head; teeth very sh(ji't and slender, but somewhat longer than those in //. aiUr:ni!i and //. siriatulus, 

 arranged in narrow bands in l:)Oth jaws, the inner series evidently longer than the outer but still very 

 small; all the teeth are depressible; with a lens they are seen to lie arrow-shaped at tip; barbel wanting; 

 eye small, shorter t ban snout, and liut half width of interorbital sjiace; preopercle very widely expanded, 

 its angle broadly rounded, its upper lind) ol)li(iue and convexly curved; around preopercular angle 

 the margin is rather coarsely crenate; gill-membranes moderately joined anteriorly, wdiolly free from 

 isthmus; gill-slits wide, the membranous attachment to the first arch encroaching lesson anterior cleft 

 than in species of Miirruiinia; a narrow slit behind fourth arch; gill-rakers short, sessile, spinoiis; in 

 uninjured specimens the tail is extremely slender. 



As in related species, the first dorsal spine is minute, not evident to the eye; the second spine 

 very slender and wholly smooth, tapering to a very fine point, but not filamentous; the succeeding ray 

 unbranched, but articulated, the 4 following rays forked for a short distance near their tips; other rays 

 simjile, unliranched; rays of second dorsal very small, l>ut origin of fin can be made out without diffi- 

 culty; interspace between dorsals equal to 2.4 times base of anterior dorsal; second dorsal sjiineO.O length 

 of head; origin of anal fin vertically behind first dorsal for a distance equaling diameter of pupil; anal 

 I'ays high, 0.3 length of head; vent immediately in front of first anal ray; pectoral narrow and long, one 

 of the upper rays elongate, reaching vertical of ninth anal ray, 0.6 length of head; outer ventral ray a 

 long slender filament, reaching the same vertical as pectoral filament, 0.7 length of head; ventrals 

 inserted in advance of pectoral base Ijy a distance equaling diameter of pupil. 



Scales large, very thin and caducous, round in outline, with parallel concentric lines whose centers 

 coincide with those of the scales; no spines on any of the few scales examined, these including all the 

 scales of the breast, a few above and behind bases of ventrals, those between pectorals and ventrals, 

 those behind and above bases of pectorals, and one above bases of anterior anal rays; the scales evi- 

 dently covered the entire body in life, but may have been absent on head. 



