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 length 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-slit 

 is less restricted than usual in this subfamily; about 13 short and 

 spinous gill-rakers were counted on the first arch. 



The anus is located immediately before the anal fin, at a distance 

 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 types). . 



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 

 buccal 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 H. aterrimus 1 and to H. papy- 

 raceus 2 forming with them the group which we have just called 

 Papyrocephalus. H. harbatulus 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 harbatulus 

 there are but 7; in papyraceus, 11; in aterrimus, 13 or 14. 



{harbatulus, in reference to the short barbel.) 



1 Gilbert, Bull. U. S. Fish Comm.. 1903 (1905), sec. 2, p. 666, pi. 93 (Hawaiian Islands). 

 2 .Tordan and Gilbert, Bull. II. S. Fish Comm., 1902 (1904), p. 614, text figure (Sagami 

 Bay, Japan). 



