BULLETIN OF THE UNITED STATES FISH COMMISSION. 53 



This species is known to us only from the descriptions of Giinther 

 and Steindachner. 



20. Alius hypophthalmus Steindachner. 



Ariua hypophthalmus Steindachner Iclith. Beitr. iv, 31, 1875, taf. x, (Panama). 



Habitat. — Pacific coast of Central America; Panama. 



Head 3f (4); depth 4§- (5|); width of head 5£j length (29508) 14 

 inches. D. I, 7; A. 2, 20. 



Body elongate, compressed, the hack rather abruptly elevated at 

 front of base of dorsal. Head rather long, narrow, much depressed an- 

 teriorly, as high at occiput as broad. Snout rather narrow and thin, 

 rounded anteriorly; the mouth small, the upper jaw much projecting. 

 Eye small, placed low, with no vertical range, its middle below the level 

 of angle of mouth, 7 in head; interorbital space 2-J- in head; breadth of 

 mouth 2^ ; length of snout 3. 



Palatine teeth small, bluntly conic, almost granular; vomerine bands 

 of teeth separated by a very wide interval about equal to eye; on each 

 side, fully confluent with and scarcely distinguishable from the palatine 

 band, which forms a large oblong patch rather broadest anteriorly. 

 Palatine band without backward prolongations. Both jaws very thin, 

 depressed, their bands of teeth narrow. Barbels very long and slender, 

 the maxillary barbel extending nearly to middle of pectoral spine; 

 outer mental barbels nearly as long as maxillary barbel, considerably 

 longer than head, extending well past base of pectoral; inner mental 

 barbels almost reaching base of pectoral. 



Ante-dorsal shield very short, narrowly crescent-shaped, its length 

 on the median line scarcely more than one-fifth its width. Occipital 

 process subtriangular, somewhat emarginate behind, in the adult speci- 

 men longer than broad, its sides concave. Its sides slope steeply from 

 the median line, which forms an angle rather than a keel. A short 

 distance in front of the base of the occipital process is the pointed ter- 

 mination of the long and rather narrow fontanelle, which is widest above 

 the cheeks, tapering slowly forward and more rax>idly backward. On 

 each side of the fontanelle anteriorly is a ridge composed of a rather 

 feeble bone, striate, but not granular, and like the rest of the interorb- 

 ital space, covered with thick skin. An oblique ridge extends upwards 

 and backwards between the above-mentioned ridge and the eye, the in- 

 terorbital region being more uneven and covered by thinner skin than 

 usual in this genus. Shields of head all rugose, moderately rough, but 

 scarcely granular, the depressions being rather of the nature of reticu- 

 lating furrows ; young specimen with the plates more granular. Oper- 

 cle with distinct radiating stride. Gill-membranes forming a very narrow 

 fold across the isthmus. 



Dorsal spine long, 1£ in head, considerably longer than the pectoral 

 spine. Axillary pore well developed. Humeral process very short, nearly 

 smooth, less than one-fourth length of pectoral spine. Adipose fin rather 

 high, its posterior margin largely free. Upper lobe of caudal short, 



