344 MEMOIRS OF THE CARNEGIE MUSEUM 



Gill-membranes free from the isthmus; gill-rakers about 5-10. 



Lateral line complete, decurved; a very narrow sheath composed of one series 

 of minute scales along the bases of the first ten anal rays. Caudal lobes entirely 

 naked; preventral region broadly rounded; predorsal and prevcntral areas each 

 with a median series of scales; postcentral area compressed; dorsal and ventrals 

 equidistant from tip of snout; origin of anal entirely behind dorsal; adipose fin 

 slightly in advance of end of anal; pectorals not or scarcely to ventrals; ventrals 

 not to anal, with a small axillary scale. 



Alimentary canal about equal to the length (without the caudal), with eleven 

 large cceca; air-bladder large, the posterior portion more than twice as long as the 

 anterior, not quite reaching anal. 



Key to the Guiana Species of Cbeatochanes. 

 a. Maxillary extending to end of the second suborbital, its tip and posterior margin of pupil equidistant from 

 tip of snout; suture between first and second suborbital usually extending down and back; second 

 suborbital short, its anterior margin continued as one convex curve to the angle; normally seven, 

 rarely eight, rows of scales between the lateral line and the dorsal; stride of scales when present nearly 

 parallel. 

 b. Caudal lobes dark, the upper darkest, with water-marks; basal spot of upper caudal lobe, as well 

 as dorsal and anal rays, yellow; pectorals not reaching ventrals; second tooth of the pre- 

 maxillary in line with the rest or moved forward; lateral stripe (in formalin specimens) dimin- 

 ishing in front of the dorsal, not continued to the head: very highly iridescent. Head 3.8-4; 



depth 3.7.5; D. 11 ; A. 26-29; scales 7-44 to 47-2.5 or 3 affinis. 



bb. Caudal lobes plain, a broad black band on about' eight rays of the caudal, counting from the second be- 

 low the middle upward, margined with red above and below; pectorals just reaching ventrals; 

 second tooth in line with the rest or slightly withdrawn. Head 4-4.25; depth 3.4-3.5; D. 11; 

 A. 27-29; scales 7-44 to 46 (usually 45)-3; eye 2.4-3; interorbital a little greater or a little less 



than eye; maxillary with one or two teeth melanurus. 



an. Maxillary not extending to end of second suborbital, its tip and middle of eye equidistant from tip of 

 snout ; suture between first and second suborbital vertical; lower jaw shorter; anterior margin of second 

 suborbital not forming a simple convex curve to the angle above the angle of the preopercle. Nor- 

 mally six. very rarely seven, scales between the lateral line and the dorsal; upper caudal spot, as 

 well as dorsal and anal rays, red; middle caudal rays and upper lobe beyond the red spot black, with 

 water-marks; second tooth of the front row of the premaxillary withdrawn; pectorals shorter than in 

 affinis, not reaching the ventrals; lateral stripe (in formalin specimens) continued to the head; less 

 highly iridescent in life than affinis. Head 4.66-4.75; depth 3.4-3.8; D. 11; A. usually 31 (28-31); 

 scales 6-45 or 46-3; articulation of lower jaw slightly in advance of the suture between the first and 

 second suborbital; maxillary teeth 0-2 caudomaculatus. 



