47 



lar casque, and perhaps by the forked posterior extremity of the 

 lateral line. We have not been able to examine any representatives 

 of the group, and cannot say in what other respects it may differ. 

 Bleeker alludes to the resemblance of the single genus to the re- 

 stricted genus Arius. 



Group PiMELODI Gill. 



Supramaxillary and two pairs of inframaxillary barbels only 

 present. Anal fin short, commencing some distance behind the anus. 



§ 1. Body slender. 



Head subcorneal in profile, above gradually narrowed to the little 

 rounded or subtruncated muzzle ; skin tense and very thin, not con- 

 cealing the sculpture of the cranium. 



Eyes generally large and suboval. Adipose fin elongated, thin, 

 and compressed, vertically striated, posteriorly truncated. 



Caudal fin forked, with the inferior lobe generally longest. 



Genus Pimelodus (Lac.) Gill. 



SYNONYMY. 



Pimelodus (sp.) Lacepede, Hist. Nat. des Poi^sons, vol. v. pp. 94, 



107. 

 Rhamdia (sp.) Bleeker^ Ichthyologiae Archipelagi Indici Prodromus, 



vol. I. Siluri. 



Supraoccipital bone, continued backward as a stout process, the 

 apex of which is emarginated, and receives the subacute anterior 

 portion of the head of the second interspinal. Anterior dorsal fin 

 armed with a well-developed spine. 



The genus Pimelodus^ as now restricted, only includes certainly the 

 Pimelodus maculatus of Lacepede. Two or three doubtful species 

 may possibly be also referred to the genus, when they are better 

 known. 



Type Pimelodus maculatus Lacepede. 



This species is found in the La Plata, Parana, and Uruguay rivers, 

 and as far south as the 26th degree of latitude in South America. 



Genus Rhamdia Bleeker. 



SYNONYMY. 



Mystus (sp.) Gronovius, Museum Gronovianum, vol. i. 



Heterobranchus (sp.) Spix. 



Pimelodus (sp.) Cuv. et Vcd. Hist. Nat. des Poissons, vol. xiv. 



Pteronotus Swainson, Nat. Hist, of Fishes, &c., vol. ii. 



Rhamdia Bleeker, Ichthyologiaa Archipelagi Indici Prodromus, vol. i. 



Siluri, pp. 197, 204. August, 1858. 

 Pimelenotus Gill, Synopsis of fresh-water fishes of Trinidad, p. ; ib. 



in Annals of the Lyceum of Nat. Hist, of New York, Sept. 1858. 



