244 Field Museum op Natural History — Zoology, Vol. X. 



Body rather robust; profile from snout to dorsal straight and gently 

 elevated in female, concave in adult males; head depressed, its width 

 I to 1.8 in its length; posterior part of body rather strongly compressed; 

 snout short, broad, about equal to diameter of eye; eye 4.4 to 6.65 in 

 head; interorbital 1.53 to 1.63; mouth broad; a pair of maxillary barbels, 

 with a bone extending to anterior margin of eye in female, almost or 

 quite to gill-opening in male; chin with 2 pairs of barbels; teeth in the 

 jaws in bands; gill-opening small; dorsal plate rather broad; humeral 

 process narrow, pointed slightly upward; dorsal spine in female some- 

 what shorter than head, notably longer than head in the male, with 

 barbels on its anterior margin, at least in young and in males; origin of 

 dorsal more than half as far from tip of snout as from tip of adipose; 

 adipose fin over posterior part of anal; caudal fin forked, both lobes 

 pointed, equal to or longer than head; anal fin rather low, with heavy 

 membrane on its base, length of its base shorter than width of head; 

 ventral fins reaching origin of anal; dorsal fin not nearly reaching base 

 of ventrals, the spine usually about equal to length of head. 



Color dark above, pale below; sides variously spotted or marked with 

 black. Usually with a dark spot or elongate blotch on middle of side 

 below dorsal ; some specimens with roundish black spots on sides of head 

 and caudal peduncle. Fins unmarked. Our largest specimen much 

 darker than the others. 



There are 8 specimens in the present collection, ranging in length 

 from 87 to 192 mm. All are from the lower Rio Tuyra. One specimen 

 is from several miles above and the others from several miles below the 

 head of the tide. 



This species is very closely related to T. fisheri Eigenmann, from 

 which it differs mainly in the shape of the caudal, which has a much 

 more concave margin, and longer and more pointed lobes. It also 

 differs from the latter in the more posterior position of the dorsal and 

 in the shorter anal. 



Habitat: Rio Tuyra Basin. 



5. Genus Ageneiosus Lac6p^de. 



Ageneiosus Lac^p^de, Hist. Nat. Poiss., V, 1805, 132 (type Agenetosus 



armatus Lac^p^de). 

 Pseudageneiosus Bleeker, Nederl. Tijdschr. Dierk., I, 1863, 108 (type 



Ageneiosus hrevi fills Cuvier & Valenciennes). 



Body elongate; snout much longer than eye, with maxillary barbels 

 only; eyes lateral; the orbit without a free margin; occipital process 



