48 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



fontanelle, which is somewhat widened anteriorly, finally merging into 



the broad, flat, smooth interorbital area, the boundaries of which are 

 not well defined ; shields of head unusually smooth, all finely and very 

 sparsely granular, the granules not forming distinct lines. 



Gill-membranes forming a rather broad fold across isthmus. 



Dorsal spine long, usually, but not always, shorter than the pectoral 

 spine, about If in head ; axillary pore absent. Humeral process rather 

 broadly triangular, not much produced backward, less than half length 

 of pectoral spine, its surface not granular, covered by skin. Adipose 

 fin half length of anal, its posterior margin little free. Upper lobe of 

 caudal longest and somewhat falcate, about as long as head. Ventral s 

 about reaching anal in the females, shorter in the males. Vent much 

 nearer base of ventrals than anal. 



Color olire green, with bluish luster, white below; upper fins dusky 

 olivaceous; caudal yellowish dusky at tip ; anal yellowish with a median 

 dusky shade ; ventrals yellowish, the basal half of the upper side ab- 

 ruptly black ; pectorals similarly colored, the black area rather smaller; 

 maxillary barbel blackish ; other barbels pale. 



Very common at Mazatlan, where it is the most abundant species of the 

 genus. It reaches a length of less than 18 inches. It was not observed 

 at Panama by Mr. Gilbert. According to Giinther and Steindachner 

 this species occurs on both sides of the isthmus. It is not improbable 

 that Arius seemani and ccerulescens Gthr. are identical with it. Our 

 specimens answer the description of assimilis better than that of either 

 of the others. 



SPECIMENS IN UNITED STATES NATIONAL MUSEUM. 



231G1. Mazatlan. Gilbert. 



28189. Mazatlan. Gilbert. 



28210. Mazatlan. Gilbert. 

 28213 (2). Mazatlan. Gilbert, 



28221. Mazatlan. Gilbert. 



28232. Mazatlan. Gilbert. 



28276. Mazatlan. Gilbert. 



28301. Mazatlan. Gilbert. 



14. A.rius caerulescens Giinther. 



Arius ecerulescens Giinther, Cat. Fishes Brit. Mus. v, 149, 1864 (Rio Htiamnclial ; west 

 coast of Guatemala). 



Habitat. — Pacific coast of Central America; Eio Huamuchal. 

 This species is unknown to us. It is certainly very close to Arius assim- 

 ilis, if not identical with it. 



15. Arius guatemalensis Giinther. 



Arius (/it at- main/six Giinther, Cat. Fibh. Brit. Mus. v, l c 64, 145 (Guatemala; 

 Chiapam); Giinther, Fish. Centr. Auier. 1869, 393 (name only): not Arius 

 guatemalensis Steind. 



Habitat. — Pacific coast of tropical America ; Mazatlan ; Chiapam. 



