210 MEMOIRS OF THE CARNEGIE MUSEUM 



lower heavier; no teeth; barbels all broadly fringed, the maxillary barbel about 

 reaching tip of pectoral. 



The four mental barbels but little shorter than the maxillary ; gill-membranes 

 widely separate, gill-rakers very numerous, 2-2.5 times as long as eye. 



Dorsal small, nearer adipose than to tip of snout, widely separate from the 

 occipital crest; base of adipose 1.5 times as long as eye; caudal forked; pectorals 

 reaching to or beyond tips of ventrals and beyond origin of anal; anal very long, 

 about 2 in the length. Upper part of head and sides above lateral line steel-blue, 

 white below; pectoral, dorsal, and caudal dusky; anal white or nigrescent. 



Family VI. PYGIDIID^. 20 



> Siluroidei trichomycteriformes Bleeker, Nederl. Tijdschr. Dierk., I, 1863, 112. 



> Siluridce opisthopterce Gunther, Catalogue, V, 1864, 4. 



> Siluridcv branchicolm Gunther, Catalogue, V, 1864, 4. 



= Tricho?nycteridcc Gill, Arrangement of the Families of Fishes, 1872, 19. 

 = Pygidiidce Eigenmann and Eigenmann, Am. Nat., XXII, 1888, 649. 

 The characters are given in the key to the families, page 119. 



Key to the Guiana Genera of Pygidiidce. 

 a. Dorsal entirely in front of the ventrals; vomer with a series of conical teeth on each side; eye without 

 free orbital margin; a maxillary and two pairs of mental barbels; each jaw with a narrow band 



of conical teeth. (CctopsiiKE.) Hemicetopsis. 



aa. Dorsal behind the ventrals; no teeth on vomer. 



6. Mouth terminal, maxillary with two barbels of about equal size; a nasal barbel; gill-membranes 



free. (Pygidiinw.) Pygidium. 



66. Mouth inferior, very wide; one of the maxillary barbels minute; no nasal barbel; gill-membranes 

 broadly united with the isthmus. (Stegophilince.) Ochmacanthus. 



Subfamily Cetopsin^e. 



Hemicetopsis Bleeker. 



Hemicetopsis Bleeker, Nederl. Tijdschr. Dierk., I, 1863, 111. 



Type, Cetopsis candiru Agassiz. 



Dorsal in front of the ventrals; teeth conical, those on the vomer in a single 



series. 



Key to the Guiana Species of Hemicetopsis. 



a. Gill-membrane very broadly united to the isthmus, the gill-opening extending as far below as above 



the pectoral; posterior margin of the eye at the end of the first third of the head; ventrals scarcely 



reaching anus; head subglobose; chromatophores of the sides with their branches spreading 



backward and forward only, not upward and downward; maxillary barbel about half as long 



as the head; Br. 10 macilentus. 



«° A family of mixed elements and hard to define. 



