eigenmann: the FRESHWATER FISHES OF BRITISH GUIANA 255 



uuu. Teeth in both jaws obliquely truncate, directed obliquely 



forward toward a median point Leporinus. 



U. (Jill-membranes free from the isthmus and from each other. 

 w. Dorsal with fifteen rays. (Crenuchince.) 



x. An adipose fin; mouth large, maxillary extending to 



below middle of eye Crenuchus. 



xx. No adipose fin; mouth small, maxillary extending to 



below anterior margin of eye Pcecilocharax. 



ww. Dorsal short. (Aphyocharacinos.) 



y. Lateral line complete; maxillary with a few teeth. 



Odontostilbe. 

 yy. Lateral line incomplete. 



2. Caudal naked; teeth pointed, with a notch on each 



side Aphyocharax. 



22. Caudal scaled Aphyodite. 



oo. Premaxillary with two or more series of notched teeth. (See A.) 

 A. Gill-membranes united, free from the isthmus. Dorsal entirely behind the ventrals, in part over the anal; 

 teeth pluricuspid incisors, a single tooth in the front row of each premaxillary; mouth small. 

 (Iguanodectince.) 



B. Breast not compressed to an edge Iguanodectes. 



BB. Breast compressed to an edge Piabucus. 



A A. Gill-membranes free from each other and from the isthmus; opercle not prolonged. 



C. No predorsal spine. 



D. Preventral area with a median edge; pectorals small, placed low; anal basis nearly horizontal; 



mouth large, with canines. (AgoniatiruB.) Agoniates. 



DD. Preventral area rounded, sometimes very narrow. 



E. Lower jaw with a single series of teeth. {Tetragonopterinw.) 

 F. Gill-rakers setiform. 



G. Caudal scaled; anal with a basal sheath of scales. 



H. Lateral line much deeurvecl in front Tetragonopterus. 



H H. Lateral line not greatly decurved, scales entire. 



I. Lateral line complete; predorsal area with a median series of scales; five 

 teeth in the inner series of the premaxillary; second suborbital not 



completely covering the cheek Mcenkhausia. 



//. Lateral line incomplete; caudal lobes equal. 



J. Maxillary with teeth along its entire margin Pristella. 



J J. Maxillary with few or no teeth Hemigrammus. 



GG. Caudal naked. 



K. Preventral area with several series of normal scales. 



L. Lateral line incomplete. Maxillary border a simple curve; origin of anal 

 behind origin of dorsal; scales cycloid. 



M. Pectoral normal Hyphessobrycon. 



MM. Pectoral archaic, a fleshy lobe surrounded by a fringe of filaments. 



Dermatocheir. 

 LL. Lateral line complete. 



iV. Maxillary border meeting premaxillary border at a right angle, its 



