eigenmann: the FRESHWATER FISHES OF BRITISH GUIANA 135 



Sciadeichthys Bleeker, Ichth. Arch. Ind. Prodr., I, 1858, 62, 66 {emphysetus) , 



not Sciadeiehthys Bleeker, Nederl. Tijdschr. Dierk., I, 1863, 99. 



Type, Bagrus emphyselus Mtiller and Troschel. 



This genus is distinguished from other South American Silurids by the approxi- 

 mate nares, the enlarged dorsal plate, the backward projecting angle of the palatine 

 patches of teeth, and the absence of an internarial membrane. The species are 

 indiscriminately called " gillbacker." 



Only four species were secured, but several others found at Cayenne may 

 occur occasionally or seasonally in Guiana. 



Key to the Species op Sciadeichthys. 

 a. Teeth on the palate villiform or bluntly conical. 



6. Dorsal plate pointed in front, entering the notched occipital process. 



c. Eye 8 in interorbital; dorsal plate as wide as the cranium behind the eye; granulations not 



extending forward to eyes flavescens. 



cc. Eye 4 in interorbital; dorsal plate much narrower than the cranium behind the eye, its sur- 

 face striate; maxillary barbel reaching past origin of ventrals emphysetus. 



66. Dorsal plate notched in front, receiving the point of the occipital process. Eye nearer snout 

 than to preopercle; jaws subequal; occipital process broader than long, mucronate at tip. 



Eye 1.25 in snout proops. 



aa. Teeth on the palate granular parked. 



14. Sciadeiehthys flavescens (Cuvier and Valenciennes). (Plate V, fig. 1.) 

 Bagrus flavescens Cuvier and Valenciennes, Hist. Nat. Poiss., XIV, 1839, 462 



(Cayenne).— Kner, SB. Akad. Wiss. Wien, XXVI, 1857, 386 (locality?). 

 Arius flavescens Gunther, Catalogue, V, 1864, 151 (copied). 



Galeichthys flavescens Jordan, Proc. U. S. Nat. Mus., IX, 1886, 559 (name only). 

 Tacliisurus flavescens Eigenmann and Eigenmann, Proc. Cal. Acad. Sci., (2), I, 



1888, 141 (name only); Occasional Papers Cal. Acad. Sci., I, 1890, 53. 

 Sciadeichthys flavescens Jordan and Evermann, Bull. U. S. Nat. Mus. No. 47, I, 



1896, 123. 



The head of a specimen of this species was secured in the Georgetown market. 

 It measures 305 mm. to the dorsal. (C. M. Cat. No. 1265.) 



15. Sciadeichthys emphysetus (Mtiller and Troschel). (Plate IX, fig. 1.) 



Bagrus (Sciades) emphysetus Muller and Troschel, Horse Ichth., Ill, 1849, 8 

 (Surinam). — Muller and Troschel, in Schomburgk, Reisen, III, 1848, 627 

 (Waini and Barima). 



Arius emphysetus Gunther, Catalogue, V, 1864, 150 (copied). 



Sciades emphysetus Bleeker, Nederl. Tijdschr. Dierk., I, 1863, 91 (name only). 



