FISHES OF THE FAMILY LOEICAEIID^. 309 



Pectoral spine extending a little beyond middle of ventral ; adipose 



fin with a small nodule imbedded in the upper half of its 



posterior part ; anal opening at j of the distance from base of 



ventral to origin of anal 10. A. chota Rgu. 



Pectoral spine extending nearly to tip of ventral ; adipose fin with 



a nodule imbedded in the upper half of its posterior part ; 



anal opening midway between base of ventral and origin of 



anal 11. A. marmoratus Rgn. 



Pectoral spine extending to tip of ventral ; adipose fin without 



nodule 12. A. longifilis Stdr. 



ft. Ventrals extending to the anal opening, barbel 

 ?-§ of the distance from its base to the gill- 

 opening, pectoral spine to middle of ventral . . 13. A. sabalo C. & V. 



j. Ventrals extending § of the distance from their 

 base to the anal opening, barbel to the gill- 

 opening, pectoral spine to posterior I of ventral . 14. A. taczanowskii Blgr. 



2. Ventrals originating below the fifth dorsal ray . . .15. A. prenadilla C. & V. 



B. Outer series of teeth of the prsemaxillaries all acutely 



bicuspid ; nasal flap not produced as a barbel ; adipose 



fin moderately developed, without trace of a spine . . 16. A. fissidens R°-n. 



C. Outer series of teeth of the prsemaxillaries all bicuspid, or 



the lateral teeth unicuspid. Nasal flap produced as a 



barbel 17. A.festos Blgr. 



D. Outer teeth of both jaws compressed, expanded, some- 



times more or less distinctly bicuspid, usually distinctly 

 incisor-like. 



Interocular width less than the distance from eye to posterior 



nostril; barbel not nearly reaching the gill-opening .... 18. A. peruanus Stdr. 



Interocular width equal to the distance from eye to posterior 



nostril; barbel extending nearly to the gill-opening . . . .19. A. simonsi Ugn. 



1. Arges homodon, sp. n. (Plate XXI. fig. 1.) 



Length of head 3| times in the total length. Interocular width a little less than 

 the distance from eye to posterior nostril, 3| times in the length of head. Outer series 

 of teeth of the praemaxillaries all bicuspid, more or less Y-shaped ; mandibulary teeth 

 bicuspid ; barbel extending beyond the gill-opening. First dorsal ray equal to | the 

 length of head ; pectoral spine extending to middle of ventral ; ventrals originating 

 well in advance of the dorsal, extending f of the distance from their base to the anal 

 opening. Spine of the adipose fin well developed, freely movable, inserted at a distance 



