242 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. X. 



origin of dorsal slightly nearer adipose than tip of snout; adipose fin 

 shorter than head, 4.8 to 5.5 in length of body; caudal fin deeply forked, 

 the upper lobe the longer; anal fin without distinct spine, its origin 

 behind origin of adipose; ventral fins inserted under posterior rays of 

 dorsal; pectoral spine with hooks on both sides in young, becoming 

 smootiier with age, i to 1.23 in head. 



Color bluish above, pale silvery below. Young with numerous round 

 specks or spots on head and side, which become fewer with age and wholly 

 disappear in specimens of 200 mm. and more in length. Fins unmarked. 



We have 8 specimens of this species, ranging in length from 142 to 

 300 mm. All are from the lower Rio Tuyra, some of them from below 

 the head of tide water. 



This fish is probably not distinct from P. clarias (Bloch) of which 

 there are at hand numerous specimens from the Rio Atrato and Rio 

 Magdalena. However, we do not find the dark spots, so characteristic 

 in the young from the Rio Tuyra, present in the specimens from the 

 more southern streams. The occipital process apparently is also slightly 

 wider in the Rio Tuyra specimens. Our specimens may, therefore, 

 be considered a variety of P. clarias with dark spots present in all except 

 the adults. 



Habitat: Rio Tuyra Basin. 



3. Genus Pimelodella Eigenmann & Eigenmann. 



Pseudorhamdia (non Bleeker) Steindachner, Sitzb. K. Ak. Wiss. Wien, 

 LXXIV, 1876, 604 (type Pimelodus lateristriga Muller & Troschel). 



Pimelodella Eigenmann & Eigenmann, Proc. Cal. Ac. Sci., 2nd. Ser., I, 

 1888, 131 (type Pimelodus cristatus Muller & Troschel). 

 This genus differs from Pimelodus in having a narrower and more 



spine-like humeral process and the fontanel extends farther back, 



notably past anterior margin of eye. Only a single species is found in 



the waters of Panama. 



3. Pimelodella chagresi (Steindachner). 



Pimelodus (Pseudorhamdia) chagresi Steindachner, Sitzb. K. Ak. Wiss. 



Wien, LXXIV, 1876, 584 (Rio Chagres and its tributaries). 

 Pimelodella chagresi Eigenmann & Eigenmann, Proc. Cal. Ac. Sci., 2nd. 



Sen, I, 1888, 134 (RioObispo), and Occ. Pap. Cal. Ac. Sci., I, 1890, 



1 60 (Rio Chagres and its tributaries). 



Head 3.8 to 4.7; depth 5.2 to 6.2; D. I, 6; A. n or 12. 



Body elongate, compressed, the dorsal region moderately elevated; 

 head rather narrow; snout tapering, 2.3 to 2.7 in head; eye 3.85 to 4.6; 



