SOUTH AMERICAN NEMATOGNATHI. 117 



Type: Pimelodus quelen Quoy & Gaimard. 



The name Rhamdia seems to be the oldest available 

 name for this genus. Notoglanis can scarcely be separ- 

 ated on account of its ten dorsal rays as quelen and sapo 

 sometimes have eight rays and hilarii occasionally has 

 nine. 



Undoubtedly on account of insufficient descriptions 

 some species have been placed here which ought to be 

 placed in Rkamdella. The young of these species usually 

 have the fontanel extending to the base of the occip- 

 ital process with a bridge behind the eye and another in 

 front of the occipital bone. The occipital fontanel 

 sometimes remains in the adult as a shallow pit from 

 which the ridges of the posterior portion of the head 

 radiate. The postfrontal fontanel usually disappears 

 entirely and in one specimen of quelen the frontal fonta- 

 nel had also disappeared. 



Habitat: Rio Plata to Mexico and Western Peru. 



DOUBTFUL SPECIES OF RHAMDIA. 



78.1. Pimelodus velifer Humboldt, Observ. Zool. ii, 

 171, 1805 (Magdalena River). The substance of the de- 

 scription is: Elongate; adipose dorsal covering the whole 

 median part of the body. D. 7; A. 10; V. 6. 



78.2. Pimelodus argentinus Humboldt, 1. c. 171, 1805 

 {Magdalena River near Chilloa). White; back bluish. 

 Maxillary barbels -| as long as the body. D. 7; V. 5; 

 pectoral and dorsal spines not serrated. 16 inches long. 



78.3. Laukidi Schomburgk, Fish. Brit. Guiana, i, 

 176, 1843. Rhamdia laukidi Bleeker, Ichthyol. Arch. Ind. 

 208, 1858 (copied). Body blue-black; belly whitish, 

 finely spotted with black. Eyes placed in middle of 

 head. Teeth a fine series, thickly set in both jaws. 

 Ventrals midway between pectorals and anal. Air 

 bladder heart-shaped. Reaches a length of 18-20 inches. 

 D. 7; A. 9; Br. 8. 



