EIGENMANN: the freshwater fishes of BRITISH GUIANA 147 



Color brownish above; sides and ventral surface silvery, sometimes with brown 



dots. 



Hexanematichthys Bleeker. 



Hexanematichthys Bleeker, Ichth. Arch. Ind. Prodr., I, 1858, 62, 65. 



Type, Bagrus sondaicus Cuvier and Valenciennes. 



Similar to Arius, but the palatine teeth villiform. The species are found largely 

 on the Pacific Coast. But one species has been taken in British Guiana. 



24. Hexanematichthys rugispinis (Cuvier and Valenciennes). (Plate IX, fig. 3.) 



Arius rugispinis Cuvier and Valenciennes, Hist. Nat. Poiss., XV, 1840, 77 



(Cayenne).— Kner, SB. Akad. Wiss. Wien, XXVI, 1857,388 (Para).— Gun- 



ther, Catalogue, V, 1864, 156 (copied). — Vaillant, Nouv. Arch. Mus. 



d'Hist. Nat., (4), II, 1900, 124 (Carsevenne, French Guiana). 

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

 Tachisurus rugispinis Eigenmann and Eigenmann, Proc. Cal. Acad. Sci., (2), I, 



1888, 145 (Para); Occasional Papers Cal. Acad. Sci., I, 1890, 83. 



Several specimens, 235-420 mm. Georgetown market. (C. ]M. Cat. No. 

 1281-1286; I. U. Cat. No. 11780.) 



Head 3.5-4; depth 5.5-6; D. I, 7; A. 19-21. Eye 3 in snout; 3.5 in inter- 

 orbital, 10 in head. Slender, tail compressed. Head broad and depressed, tapering 

 forward; width of the head 1.5-1.4 in its length, at the angle of the mouth 2.4-2.5; 

 depth of head 1.6-2; profile rather steep. Top of head, humeral process, front 

 and sides of the spines, and dorsal plate granular, the granulation not extending 

 forward to above middle of cheeks. Occipital process triangular, about as long 

 as broad, the median ridge not very prominent. Middle of the fontanel behind the 

 eye, the posterior portion separated by a bridge, not continued backward as a 

 groove; interorbital region with four ridges. 



Barbels villiform; maxillary barbel reaching to or beyond base of pectoral, 

 post-mental to gill-opening, mental barbels much shorter. 



Mouth inferior, lower jaw included, lips thick; teeth villiform, the anterior 

 ones in the jaws longer, depth of the premaxillary band 4 in its width; palatine 

 patches of teeth one diameter of the eye apart, the width of the patches less than 

 one diameter of the eye. 



Gill-membranes meeting in an angle, forming a fold across the isthmus. Gill- 

 rakers 6 + 11. Pectoral pore none; vertical series of pores present. 



Distance of dorsal spine from the snout 2.33-2.5 in the length. Space between 

 dorsal and adipose fins 4-4.66 in the length. Adipose fin adnate, as long as the anal 

 fin. Ventrals 2.5 in the head; pectoral spine serrate behind. 



