od 
THE AMERICAN TETRAGONOPTERINAE. 103 
25. MOENKHAUSIA LEPIDURA GRACILIMA Eigenmann. 
Plate 101, fig. 7. 
Moenkhausia lepidurus gracilimus EIGENMANN, Bull. M. C. Z., 1908, 52, p. 104 (Serpa); Rept. Princeton 
univ. exped. Patagonia, 1910, 3, p. 438. 
Hasirat.— Serpa. 
20983 Cotypes 21 About 39-57 mm. Serpa Thayer 
Anal on an average with twenty-two rays, there being one with nineteen, 
two with twenty, one with twenty-one, eleven with twenty-two, four with 
twenty-three, one each with twenty-four and twenty-five; pectoral not reaching 
ventrals. 
Depth 4 or nearly 4, the greatest depth just behind pectorals, then tapering 
gradually to caudal. The fontanel, in the long, slender ones with a typically 
colored caudal, is narrower than in the others. Lateral line 35 or 36. 
Color of caudal as in typical individuals of M. lepidura, but faint, with a 
dusky shade extending on the lower caudal lobe. 
Humeral spot, even in the smallest, of over twenty chromatophores, not 
well defined. 
20717 17 47-59 mm. Villa Bella Agassiz 
These specimens are nearest those from Serpa. They have, on an average, 
twenty-two anal rays. Five have twenty-one, five twenty-two, and four twenty- 
three; the pectoral does not reach the ventrals. Depth 3-4; lateral line 35 or 
36. Middle caudal rays and distal part of all the remaining rays as well as 
the upper and lower margin of the fin dusky; tip of anal lobe sometimes milk- 
white; humeral spot of many chromatophores, extending up from the second 
and third or third and fourth scales. 
These specimens are appreciably different from typical M. lepidura graci- 
lima, but gradations between them are almost perfect. 
26. MoENKHAUSIA COLLETTII (Steindachner). 
Plate 8, fig. 1; Plate 15, fig. 4; Plate 101, fig. 3. 
Tetragonopterus collettii SrEINDACHNER, Flussf. Siidamer., 1882, 4, p. 33, pl. 7, fig. 3, (Obidos; Hyavary); 
EIGENMANN & EIGENMANN, Proc. U.S. N. M., 1891, 14, p. 53; Unrey, Ann. N. Y. aead. sci., 1895, 
8, p. 81. 
