210 MEMOIRS OF THE CARNEGIE MUSELM 



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 verj^ 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^..^" 



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



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



> SiluridcB branchicolce GtJNTHER, Catalogue, V, 1864, 4. 



= Trichomycteridce. Gill, Arrangement of the Families of Fishes, 1872, 19. 

 = Pygidiidoe 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 Pygidiid.e. 

 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. ( Cetopsince.) 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. ( Pygidiince.) Pygidium. 



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

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



Subfamily Cetopsin^. 

 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 

 rcacliing 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, 



