Pearson: Fishes of the Rio Beni Basin 
29 
Subfamily prochilodin^e. 
Prochilodus nigricans Agassiz. 
17286, 22, 155-175 mm., Tumupasa. Dec., 1921. 
17287,2, 230 and 240 mm., Charquiti River, Lower Bopi. Aug., 1921. 
Prochilodus beni Pearson, sp. nov. Plate IX, fig. 2. 
17288, 1, 58 mm., Cachuela Esperanza. Mar., 1922. 
Characterized by its deep body and arching profile. 
Head 3%; depth 2y%; D.12; A.12; lateral line 11-48-7; 
eye 3 ; interorbital 2 ; snout depressed ; naked portion of the 
cheek about 2 times as wide as the suborbital ; operculum with 
many fine concentric lines; postventral area with a median 
keel ; head only slightly rounded on top ; the eyes parallel with 
the sides of the body; dorsal rounded, the highest rays equal 
to the length of the head; the dorsal when depressed scarcely 
touching the adipose ; anal slightly emarginate, the second and 
third rays the longest, reaching caudal fulcra when de- 
pressed ; pectorals not quite reaching base of ventrals ; ventrals 
not near reaching anal opening; scales cycloid. 
Body with about 12 distinct transverse bars, the third to 
the seventh extending below the lateral line, the dorsal spots 
forming about 6 horizontal cross bars, the spots discontinuous 
at the middle of the interradial membrane; the caudal dusky 
with indistinct irregular dark spots ; the other fins unmarked. 
Subfamily anostomatinje. 
Laemolyta fascia ta Pearson, sp. nov. Plate X, fig. 1, 
17355, 2 cotypes, 20 mm., Lagoons, Lake Rogoagua. Nov., 1921. 
The specimens are immature and the characters hard to 
determine. If the characters hold good in the adult they 
should be made a new genus. 
Head 3 and 3.1; depth 3.5 and 3.65; D.12; A.12 and 13; eye 
31 / 2 ; lateral line 36, 9 V 2 scales in a transverse series ; snout 
short, equal to the diameter of the eye, ovate in cross-section ; 
fontanel long, wide, interrupted above the posterior margin 
of the pupil; occipital process extending 1/5 of the distance 
from its base to the dorsal ; mouth obliquely subvertical ; 
maxillary small, vertical or sloping backward, without teeth; 
premaxillary with 4 tricuspid teeth, the outer cusps small, 
often obscure, the middle cusp broadly rounded ; mandible with 
