EIGENMANN: THE FRESHWATER FISHES OF BRITISH GUIANA 131 



qq. Caudal forked. 



r. Anal of eighteen or more rays Acentronichthys. 8 



rr. Anal of about eleven rays. Premaxillary band of teeth with a 



backward projecting angle Chasmocranus. 



II. Orbit with a free margin. Head distinctly longer than broad, 

 s. Occipital process not reaching the dorsal plate. 



t. Fontanel not continued behind the eye; a small pit or fontanel some- 

 times at the base of the occipital process Rhamdia- 



tt. Fontanel continued to base of occipital process. A dorsal and a 



pectoral spine Rhamdella.' 



ss. Occipital process reaching the dorsal plate; adipose fin longer than high. 

 u. Occipital process narrow; fontanel to base of occipital process; 



humeral process spine-like Pimelodella. 



uu. Occipital process tapering; fontanel not continued behind the eyes; 

 humeral process broad, not spine-like. 



v. Caudal deeply forked Pimelodus. 



vv. Caudal obliquely rounded Gceldiella. 



jj. Teeth on vomer in moderate or large patches. 

 w. Barbels not band-like. 



.r. Head as broad as long. D. 1,7. Upper surface of head with vermiculating 

 ridges. Vomerine patch of teeth large, pentagonal, contiguous to the 

 palatine patches. Occipital process large, semicircular, not meeting 

 the reniform dorsal plate, upper half of the adipose fin usually rayed. 



Phractocephalus. 



xx. Head longer than broad; inner surface of gill-covers usually with one or more 



dermal pouches. D. 1,6-8. Caudal forked or rounded. 



y. Inner teeth of the upper jaw slender and freely movable, the band scarcely 



narrowed in the middle; teeth on vomer and palatines much smaller, 



(the palatine teeth smaller than those on the vomer), villiform. 



Adipose fin equal to or longer than the anal fin; caudal deeply 



forked, the lobes pointed Brachyplatystoma. 



yy. Teeth all similar in the upper jaw and on the vomer. 



2. Head narrowed forward, its width at the mouth scarcely if any more 

 than two-thirds its greatest width; adipose fin longer than the 

 anal; lower jaw produced beyond upper Hemisorubim. 



8 The genus Acentronichthys Eigenmann and Eigenmann contains with certainty but one species, 

 the type, Acentronichthys leptos Eigenmann and Eigenmann. Heplaplerus sxirinamcnsis Bleeker may 

 belong to this genus. It is certain that the Heptapterus collettii placed here by Eigenmann and Eigenmann 

 is not an Acentronichthys, for it has a strong pectoral spine. 



An examination of the type of Heptapterus surinamensis in Leiden gives the following: 



Skull covered with thin skin, fontanel a narrow slit to base of occipital process; first dorsal ray 



just like the second, not spinous; last ventral ray and third dorsal ray about equidistant from the tip 



of the snout; A. 18; caudal with numerous accessory rays, especially on the ventral side; middle rays 



radiating, all broken, probably rounded; teeth on each pre-maxillary in a band one-half wider than deep. 



It is therefore a Heptapterus if the caudal was rounded or an Acentronichthys if it was forked. 



9 No dorsal spine; first pectoral ray spinous at its base only; upper caudal lobe longer. Rhamdia- 

 glanis of southeastern Brazil. 



