434 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



where the least distance between them is contained 3.1 (2.6 to 3.4) 

 times in the interorbital width ; posteriorly the ridges grade " into a 

 shallow, scaleless groove which is continuous with the lateral line" — 

 a condition indicated in Weber's figure of his G. acus. The postor- 

 bital ridge is curved slightly downward behind the ridge of the 

 preopercle. The infraorbital ridge is less prominent than in any 

 other species examined, with the single exception of G. (Ahyssicola) 

 macrochir. The lower angle of the subopercle is obtusely angu- 

 lated, but without the prominent sharp flap diagnostic of the sub- 

 genera Paramacrurus, Oxymaawus, and Oxygadus. The length of 

 the orbit is contained 4.2 (3.7 to 4.25) times in the head, 1.4 (1.4 to 

 1.75) times in the snout, 1.7 (1.3 to 1.6) times in the postorbital. 

 The interorbital width, least above the front of the pupil, is about 

 equal to the orbital length, being contained 1.7 (1.4 to 1.6) times in 

 the postorbital. The maxillary extends from below the middle of the 

 large nasal fossa backward to beyond the vertical from the hind 

 margin of the orbit; the length of the upper jaw is contained 2.8 

 times in the head in the type, from 2.9 to 3.3 times in the smaller 

 specimens. Length of the slender barbel, 3.75 (2.6 to 4.2) in post- 

 orbital. 



The premaxillary teeth are cardiform and are disposed in a 

 narrow band. The mandibular teeth are in two series, which be- 

 come a little irregular in large specimens; the inner of the two 

 series is enlarged. 



The sensory canal system of the head is well developed. Be- 

 tween the occipital and the postorbital ridges there is a spacious 

 cavity, on the bottom of which large sense organs are located. 

 Each of these organs lies on a scale-like neuromastic bone, the 

 two ends of which rise upward and outward as slender curved 

 rods, arching toward each other, and supporting the skin which 

 forms the roof of the sensory cavity. Where the cavity becomes 

 shallow posteriorly, behind the ridge of the pectoral girdle, its 

 floor is covered by two scales or scale-like bones similar to those 

 described by us in Bathygadus and Hy?nenocephalus. 1 Their simi- 

 larity to the structure just described is greatly increased by the 

 presence in each of slender rods passing outward to the skin. 

 These two scales or scale-like bones are of irregular outline, being' 

 convex behind ; the anterior of the two is imbricate over the second, 

 which in turn is imbricate over the normal scales. The skin lying 

 over these plates is covered with small scales, which are separated 

 by a narrow scaleless groove from the adjacent scales of the body, 

 over which the posterior plate just described is imbricate. The 

 cavity in which these neuromastic bones lie is connected by a fora- 

 men with the cavity immediately behind the orbit, and with the 



1 Proc. U. S. Nat. Mus., vol. 51, 1916, pp. 149, 186. 



