eigenmann: the FRESHWATER FISHES OF BRITISH GUIANA 257 



/S/3. Abdomen serrate behind the ventrals only. 



y. Anal bilobed Mylesinus. 



77. Anal deeply emarginate Acnodon. 



aa. Mandible with a pair of conical teeth, premaxillary teeth trenchant. 



S. Adipose fin long Metynnis. 



00. Adipose fin short, the two series of teeth of the upper jaw separated 



from each other Myloplus. 



odd. Adipose fin short; the two series of teeth of the upper ,jaw close together, 

 teeth of the outer row forming a continuous series of incisors. 



Myleus. 



jj. Teeth conical ; gill-membranes free from the isthmus. 



e. Pectorals very large; belly compressed; body long and narrow. (Cynodmdiruc.) 



f. Abdominal area much shorter than anal basis; caudal lunate; ventrals' small; pec- 

 torals reaching anal; anal with about eighty rays; dorsal over anal; scales 



cycloid Cynodon. 



ff. Abdominal area much longer than anal basis; caudal rounded; pectorals overlapping 

 ventrals; origin of ventrals about equidistant from origin of anal and upper 

 angle of gill-opening; anal with about thirty-five rays; dorsal in front of anal; 



scales ctenoid Hydrolicus. 



«. Not as under e. 



1?. No teeth on palate; snout not prolonged. (Characince.) 

 8. Both jaws with antrorse, tooth-like structures. 



t. Anal short, of fewer than thirty rays, deeply emarginate, its origin behind 

 the vertical from the last dorsal ray. Clavicle not notched to re- 

 ceive the base of the pectoral Exodon. 



u. Anal long, its origin in front of the vertical from the first dorsal ray, its 

 margin straight; clavicle with a shallow notch to receive the base of 



the pectoral Roeboides. 



88. Jaws without antrorse, tooth-like processes. 



k. Preopercle without a spine ; anal margin straight or nearly so. 



X. Scales forty to sixty in the lateral line; clavicle with a deep notch 

 to receive the base of the pectoral, the lower part of the clavicles 

 blade-like, sub-parallel ridges bounding the breast on either 

 side and ending in a spine in front and behind; premaxillary and 

 dentary with a canine at each end; two series of teeth between 

 the canines of the premaxillary, and a single series between 

 those of the mandible; anal very long, its origin in advance of 

 the vertical from the first dorsal ray. 

 m. Lateral line complete; pectoral overlapping the ventrals. . Charax. 



nil. Lateral line incomplete; pectoral archaic Asiphonichthys. 



XX. Over ninety scales in the lateral line; clavicle with a notch; lower mar- 

 gins of the clavicles forming a much less prominent ridge than 

 in Charax, without spines; origin of anal behind the vertical 

 from the first dorsal; teeth as in Charax, but an additional and 



much larger median canine on the dentary Cynopotamus. 



int. Interopercle drawn out into a prominent spine; anal margin deeply concave; 

 origin of anal behind the vertical from the origin of the dorsal. 



