EIGENMANN: the freshwater fishes of BRITISH GUIANA 257 



/3/3. Abdomen serrate beliind the ventrals only. 



y. Anal bilobed Mylesinus. 



77. Anal deeply emarginate Acnodon. 



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



6. Adipose fin long Metynnis. 



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



from each other Myloplus. 



&55. Adipose fin short; the two series of teeth of the upper jaw close together, 

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



Myleus. 

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



«. Pectorals very large; belly compressed; body long and narrow. {Cynodontinm.) 



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

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



cycloid Cynodon. 



rr- 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-openiog ; anal with about thirtj^-five rays; dorsal in front of anal; 



scales ctenoid HydroUcus. 



(t. Not as under e. 



V. No teeth on palate; snout not prolonged. {Characinw.) 

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



i. 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; cla\icle with a shallow- notch to receive the base of 



the pectoral Roeboides. 



ee. Jaws without antrorse, tooth-Uke 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 overiapping the ventrals.. Charax. 



MM. 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, lauf, an additional and 



much larger median canine on the dentary Cynopotamus. 



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

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



