eigenmann: fresh water fishes. ■ 245 



But three genera of this family are known to occur within the h'mits of 

 the area under consideration ; they are Nematogenys, Hatcheria and 

 Fygiditim. Their relationship will be seen from the following key to all 

 the genera of the family. 



a. Dorsal entirely in front of the ventrals ; vomer with teeth ; head compressed ; anterior nares 

 almost labial. Gill-membrane broadly united with the isthmus. Eye almost entirely con- 

 cealed under the skin. A single maxillary barbel ; two pairs of mental barbels. Opercles 

 unarmed. {CetopsincB.) 



b. Teeth all conical or incisor-like, those on the vomer in a single series. 



Hemicetopsis Bleeker. 



bb. Teeth on the premaxillary villiform, in a band, those on the vomer and on the mandible 



incisor-like, in a single series. Cctopsis Agassiz. 



bbb. Teeth on the premaxillary and on the mandible villiform, in bands, those on the vomer 



in a single series. Pseudocetopsis Bleeker. 



bbbb. Teeth all villiform, in bands. Paracetopsis Eigenmann & Bean. 



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



c. Gill-openings broad, the gill-membranes almost free or forming a free membrane across 



the isthmus. [Pygidiincs.) 



d. Anal short ; eyes superior ; mouth terminal ; gill-membranes free or almost free from 

 the isthmus. 

 e. Ventrals present. 



/. A single maxillary barbel ; opercles and preopercle unarmed. 



g. Nasal barbels present ; dorsal placed over the ventrals ; one pair of 



mental barbels. Nanatogenys Girard. 



gg. Nasal barbels obsolete ; dorsal placed behind the ventrals ; two pairs 



of mental barbels. Pariolins Cope. 



ff. Two maxillary barbels ; opercle and preopercle with osseous prickles ; 



nasal barbels present. 



li. Caudal peduncle broad ; caudal with numerous accessory rays. 



Pygidium Meyen. 

 lili. Caudal peduncle slender ; caudal with very few accessory rays ; 

 dorsal emarginate. Hatcheria Eigenmann. 



ee. Ventral fins none ; otherwise like Pygidiuvi. Eremophilus Humboldt. 



dd. Anal long, partly in front of the dorsal ; head greatly depressed ; eyes infringing 

 on the upper and lower surfaces of the head; mouth inferior; gill-membranes 

 broadly joined to each other, free from the isthmus ; opercle and preopercle with 

 osseous prickles ; a series of fine labial teeth. Tridens Eigenmann & Eigenmann. 

 cc. Gill-membranes confluent with the skin of the isthmus, the gill-opening a narrow slit in 

 front of the pectoral ; opercle and preopercle armed with spines ; vent far behind the 

 middle of the body ; anal short. {Stegophilince^ 



i. Upper lip with several series of numerous small, movable teeth ; each jaw with sev- 

 eral series of minute teeth ; mouth inferior. 

 j. Gill-membranes broadly united with the isthmus. 



