522 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 
position on the midventral line; * the large size and subterminal posi- 
tion of the mouth; the development of the sensory canal system ? of 
the head, with thin bony septa connected by thin external mem- 
branes; * the large size and thinness of the scales; and the correlated 
position of the anus (immediately before the anal fin) and the num- 
ber of branchiostegal rays (7). 
44. HYMENOCEPHALUS GRACILIS, new species. 
Ty pe-specimen.—Cat. No. 78227, U.S.N.M., 96 mm. long to end of 
pseudocaudal, 29 mm. long to anus; dredged by the steamer Albatross 
at station 5292, in the China Sea off southern Luzon (lat. 18° 28’ 45’ 
N.; long. 121° 01’ 12’’ E.) ; depth, 162 fathoms; bottom temperature, 
52.4° F, 
Fin-rays—first dorsal, II, 10; pectorals, 13; ventrals, 8. 
The form of the body is entirely similar to that of H. tenuis. It is 
slender throughout, the depth gradually decreasmg toward the end 
of tail; the width of the head, equal to the greatest depth of either 
head or body, is contained twice in length of head. The sides of the 
head are strongly convex; the head in cross section is round, instead 
of rectangular as in ZZ. striatissimus. The snout projects forward be- 
yond the tip of the premaxillaries a horizontal distance half as long 
as the pupil; preocular length of snout, 1.4 in length of orbit, 3.2 in 
length of head. The orbit is oval in outline; its length is contained 
1.25 times in the postorbital, or 2.9 times in the entire length of head. 
The middle of the length of the head is at the hind margin of the 
pupil. The orbit encroaches medially upon the interorbital, the sides 
of which, in consequence, are strongly concave; the least interorbital 
width is contained about 5 times in the head, being not much more 
than half the orbital length; least suborbital width, 0.5 length of 
orbit. The mouth is large and a little oblique; the upper jaw, which 
extends backward to a vertical intersecting the eye behind the pupil, 
is contained 2.25 times in the head. The small teeth are arranged in 
narrow bands in the two jaws. The preopercular ridge, as in fenwis, 
is rounded at its angle, not being acutely produced backward as in 
the subspecies of striatissimus; the preopercular margin is widely 
rounded, and but little produced backward. The head, as in tenuis, 
is comparatively firm, and the sensory canals, though spacious, are 
much less developed than in such species as striatissimus; these 
canals are covered over by delicate membranes supported by thin 
bony septa. 
The gill-membranes, free from the sides of the isthmus, extend for- 
ward to below end of maxillary, where they form a narrow free fold 
1 Somewhat similar and doubtless homologous structures occur in other genera, par- 
ticular in certain species of Ventrifossa, such as V. nigromarginata (q. v.). 
2 The head is firmer in Hymenogadus than usual in the other groups. 
’In this character Hymenocephalus is approcahed by certain species of Ventrifossa. 
