Pearson : Fishes of the Rio Beni Basin 
33 
Aphyocharax alburnus (Gunther). 
17215, 143, 38-80 mm., Rio Iniqui, Upper Beni. Sept., 1921. 
17216, 42, 34-65 mm., Rurrenabaque. Oct., 1921. 
17342, 11, 32-43 mm., Rurrenabaque. Oct., 1921. 
17217, 3, 50-55 mm., Cachuela Esperanza. Mar., 1922. 
17218, 4, 38-45 mm., Huachi. Aug., 1921. 
17219, 8, 42-60 mm., Popoi River, Upper Beni. Sept., 1921. 
17217, part of 17218, and 17219 are all like the typical A. 
alburnus. 17215, 17216, part of 17218, and 17342 differ by 
having* 2 or more bifid teeth in the premaxillary and 6 to 8 
similar teeth in the mandible; the maxillary is intermediate 
in length between that in A. dentatus and alburnus. I have 
considered this difference an environmental one due to the 
food of the young. 
Aphyocharax amisitsi Eigenmann & Kennedy. 
17336, 2, 26 mm., Lagoon near Reyes. Oct., 1921. 
Heretofore described only from the Paraguay system. 
Prionobrama filigera (Cope) . 
17208, 20, 40-47 mm., Lake Rogoagua. Nov., 1921. 
17209, 51, 40-55 mm., Rurrenabaque. Nov., 1921. 
These specimens possess a few more anal rays than the 
typical P. filigera. Specimens taken at random give the fol- 
lowing counts. 
33 
34 
35 
36 
37 
38 
39 
17208 from Lake Rogoagua 
1 
1 
2 
5 
1 
17209 from Rurrenabaque 
6 
4 
4 
5 
1 
Megalamphodus rogoaguse Pearson, sp. nov. Plate X, fig. 3. 
17348, 1, type, 23 mm., Lagoons, Lake Rogoagua. Nov., 1921. 
Similar to M. eques from which it differs in having fewer 
anal rays and in coloration. 
Head 3.5; depth 2.6; D.ll; A. 27 ; scales 32, 10 1/2 in a ver- 
tical series; eye 2.6, greater than the interorbital; maxillary 
not quite as long as the eye, not reaching the suture between 
the second and third suborbitals; premaxillary with 7 or 8 
conical or feebly notched teeth ; maxillary with 2 teeth ; man- 
dibular teeth conical or with a single notch ; third suborbital in 
