540 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 
little wider than the suborbital; its length is contained two times in 
the postorbital, or four times in the entire length of the head. The 
middle of the length of the head lies between the hind margins of 
the pupil and of the orbit. The mouth is large, terminal, and 
oblique; the leneth of the upper jaw enters twice into the head. 
Fine teeth are arranged in very narrow bands on the jaws. The 
barbel is evident, but decidedly shorter than the pupil. The dis- 
tance between the angle of the preopercular ridge and the mar- 
gin of the preopercle is equal to the orbit. The sensory canals are 
much wider but shallower than in typical species of Hymeno- 
cephalus; the bones are excessively delicate and papery. The gill- 
membranes are free from the sides of the isthmus; the first gill-sht 
is less restricted than usual in this subfamily; about 18 short and 
spinous gill-rakers were counted on the first arch. 
The anus is located immediately before the anal fin, at a distines 
from the ventral base contained 1.6 times in the head; this distance 
is decidedly longer than that from the tip of the snout to the hind 
margin of the orbit. 
The lens-like structures on the midventral line are small; the 
one immediately in advance of the anus is double, consisting of two 
small closely connected hemispheres lying side by side, the division 
being more complete than in striatissimus. 
The few scales retained are round and wholly spineless, as in 
aterrimus, gracilis, and tenuis. 
Base of first dorsal fin, 1.7 in postorbital. The rays of the paired 
fins are weak (broken in ioe. 
Color in alcohol: blackish on the head and trunk and on the first 
dorsal and the ventral fins, becoming brown on the tail, with a black 
spot at the base of each anal ray; the pectoral fin is dusky. The 
buceal cavity is black along the margins of the jaws, but light on 
the tongue and silvery on the roof of the cavity: the branchial cavity 
is lined with dusky, the peritoneal cavity with black (underlain with 
silvery). 
The striated region is confined to the sides of the isthmus and to 
the area immediately above and behind the ventral fins. 
This species is closely related to 7. aterrimus' and to H. papy- 
raceus® forming with them the group which we have just called: 
Papyrocephalus. H. barbatulus agrees with papyraceus in the pos- 
session of a small barbel, which is lacking in aterrimus. The number 
of ventral rays serves to distinguish all three species: in barbatulus 
there are but 7; in papyraceus, 11; in aterrimus, 13 or 14. 
(barbatulus, in refer ence to the short barbel.) 
1 Gilbert, Bull, U. ie Fish Gara 1903 (1905), sec. 2, p. 666, pl. 93 (Hawaiian Islands). 
2 Jordan and Gilbert, Bull. U. S. Fish Comm., 1902 (1904), p. 614, text figure (Sagami 
Bay, Japan). 
