SOUTH AMERICAN NEMATOGNATHI. 21 



being the oldest name adopted during the binomial era, 

 must be substituted. 



This genus is characterized by the increased number 

 of caudal vertebrae. The anal is very long, being almost 

 co-extensive with the tail. Barbels 6, short. The belly 

 of the females, during the breeding season, is covered 

 with short tentacles, to which the eggs are attached. 

 The pectoral spine is broad, depressed; its inner margin 

 with introrse teeth which are strongest at the tip; 

 its outer margin with shorter extrorse teeth. 



Habitat: Guiana; Rio Para and Rio Muria. 



ANALYSIS OF THE SPECIES OF PLATYSTACTJS. 



-a. Tip of snout smooth. 



b. Sternal and abdominal region without tentacles. 



c. Barbels 6, there being no barbel at the base of the maxillary. 



(PLATYSTACTJS.) 



d. First dorsal ray not or scarcely produced. Head to gill open- 

 ing, 9 in the length, with the caudal. cotylephorus 10. 



dd. First dorsal ray produced. Head to gill opening, 10 in the 



length, with the caudal. nematophorus 11. 



cc. Barbels 8, there being a small one on the anterior margin of 



the maxillary bone; snout broad, greatly depressed, spatulate. 



(ASPREDO.) 



e. Head to tip of nuchal plate more than 4 in the length to base 



of caudal. aspredo 12. 



ee. Head to tip of nuchal plate less than 4 in the length with 



the caudal; barbels longer than in aspredo. Brownish above, 



with white dots; anal with a black margin. (Guv. & Val.) 



sicuephorus 13. 



bb. Sternal and abdominal region with a marginal series of tentacles. 

 . Barbels 8, there being a minute one on the anterior margin of the 

 maxillary bone; snout rather pointed; first dorsal ray produced in a 

 very long filament; posterior anal rays and caudal black. 



filamentosus 14. 



aa. Tip of snout with four broad spines, the inner ones fixed, belonging 

 to the ethmoid, the outer movable, belonging to the nasals. (AspRE- 

 DINICHTHYS.) tibiceu 15. 



10, Platystacus cotylephorus, 



Platystacus cotylephorus Bloch, Ausl. Fische, viii, 54, pi. 372, 1794; 

 Bloch & Schneider, Syst. Ichthyol. 372, 1801; Bleeker, Silures 

 de Suriname, 95, 1864 (Surinam); E. & E. Proc. Cal. Acad.Sci. 

 2dSer. ii, 1889, 50 (Yigia; Para; Tajapuru). 



