SOUTH AMERICAN NEMATOGNATHI. 317 



not connected with the skull by any processes or bucklers, 

 and except for its position is like that of Nematogcnys 

 and Pygidium. 



ANALYSIS OF THE GENERA OF PYGIDIID.E. 



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 concealed under the skin. 

 A single maxillary barbel; two pairs of mental barbels. Opercles un- 

 armed. (CETOPSIN^:.) CETOPSIS LVII. 

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



b. Gill-openings broad, the gill-membranes almost free or forming a free 

 membrane across the isthmus. (PYGIDIN^;.) 



c. Anal short; eyes superior; mouth terminal; gill-membranes free or 

 almost free from the isthmus. 

 d. Ventrals present. 



e. A single maxillary barbel; opercle and preopercle unarmed. 

 /. Nasal barbels present; dorsal placed over the ventrals; one 

 pair of mental barbels. NEMATOGENYS LVIII. 



ff. Nasal barbels obsolete; dorsal placed behind the ventrals; 

 two pairs of mental barbels. PARIOLIUS LIX. 



ee. Two maxillary barbels; opercle and preopercle with osseous 

 prickles; nasal barbels present. PYGIDIUM LX. 



dd. Ventral fins none; otherwise like Pygidium. 



EREMOPHILUS LXI. 



cc. 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 LXII. 



bb. 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. (STEGOPHILINJE.) 



(/. Maxillary barbel single. 



h. Teeth small, forming several series on each jaw; upper lip with 

 two or more series of movable teeth; mouth inferior. 

 i. Caudal widely forked, the upper lobe produced in a filament. 



PSEUDOSTEGOPHILUS LXIII. 



ii. Caudal rounded or slightly emarginate. 



STEGOPHILUS LXIV. 



hh. Teeth comparatively large, pointed, forming a single series on 

 the intermaxillaries only; mouth subiiiferior. VANDELLIA LXV. 



