268 THE AMERICAN CHARACIDAE. 



duced, 3.4-4 in the length; caudal deeply forked; the lower lobe distinctly the 

 longer; anal basis long, the fourth ray longest, forming with the third and fifth 

 rays a very narrow, produced lobe in the male, with its origin under the last 

 dorsal ray, slightly nearer base of pectorals than to the end of the anal. Ven- 

 trals nearly or qviite reaching anal. Pectorals beyond origin of ventrals by 2 

 scales. 



Iridescent; a well-marked vertically oval humeral spot, forming part of a 

 humeral bar, a hght bar in front of it and another behind it; a silvery lateral 

 band, a small caudal spot, not continued to the end of the middle rays although 

 the middle rays are darker than the rest. 



This species is very abimdant in the Truando. Of the numerous other 

 localities examined in which large numbers of related species were taken only 

 Quibdo yielded specimens of this species. It is possible that one of Stein- 

 dachner's specimens recorded as A. caucanus belongs here. 



Two readily distinguishable varieties were taken in the Truando. In one 

 the color-markings are strong, the iris has a dark area below the pupil and a 

 larger one above it. In the others there is no pigment below the pupil which is 

 smaller, the color is less intense but the tip of the ventrals and marginal half 

 of the anal is sometimes quite dark. It is possible that the difference in the 

 color is due to the contracted color-cells in the latter, and the expanded condi- 

 tion in the former. 



28. AsTYANAX (Zygogaster) caucanus (Steindachner). 



Plate 43, fig. 1. 



Tetragonopterus caucamts Steindachner, Ichthyol. beitr., 1878, 8, p. 71 (Cauoa); Denks. K. akad. 



wiss. Wien, 1880, 42, p. 20, pi. 7, fig. 2 (Cauca); Eigenmann & Eigenmann, Proc. U. S. N. M., 



1891, 14, p. 53; Ulrey, Ann. N. Y. acad. sci., 1895, 8, p. 273. 

 Ashjanax caucanus Fowler, Proc. Acad. nat. sci. Phil. 1906, p. 343 (Paramaribo); Eigenmann, Rept. 



Princeton univ. e.xped. Patagonia, 1910, 3, p. 433. 



Habitat. — Lower Cauca and Magdalena Rivers, Colombia. 



Specimens examined. 



