278 MEMOIRS OF THE CARNEGIE MUSEUM. 



slippery as the proverbial eel, which they resemble in other respects. The pectoral 

 gland is very large in the smaller species. 



Key to the Subfamilies and Genera of the Pygidiid.e. 



a. One pair of mental barbels, no opercular or interopercular spines; one barbel at angle of mouth; a 

 small nasal barbel; pectoral spine pungent; dorsal over ventrals. {Nematogenyince.) 



I. Nematogenys Girard. 

 oo. No mental barbels; opercle and interopercle with spines; two barbels at angle of mouth; pectoral 

 spine not pungent. 

 6. A nasal barbel; mandible with considerable antero-posterior extent, teeth along less than half its 

 total length; teeth strong; anal short; no mental barbels; opercle and interopercle with 

 spines; two barbels at angle of mouth; free-living species, some of them of economic 

 importance. ( Pygidiina:.) 

 c. Opercle with a long dermal flap; maxillary bone longer than the attached barbel; teeth nar- 

 row incisors; pectoral without a filament; anal short. ..II. Scleronema Eigenmann. 

 cc. Opercle without a dermal flap; maxillary very small. 



d. Dorsal long; caudal peduncle subterete; anal usually entirely under the dorsal; outer 



pectoral ray without a filament III. Hatcheria Eigenmann. 



dd. Dorsal shorter; caudal peduncle compressed; anal partly or entirely behind the dorsal; 

 outer ray of the pectoral prolonged or not. 



e. Ventrals present IV. Pygidium Meyen. 



ee. No ventral fins; otherwise like Pygidium V. Eremophilus Humboldt. 



bb. No nasal barbels. 



/. Mouth subterminal, the teeth strong, in a single series; gill-membranes united with isthmus; 



anal short. (Pareiodontince.) VI. Pareiodon Kner. 



//. Mouth inferior. 



g. Anal short, of 7-11 rays, its origin usually behind, rarely under that of the dorsal; lower 

 barbel at angle of mouth minute; eyes superior. Species small, some of them 

 commensals or parasites. 

 //. Mouth wide, teeth very numerous, in several very regular series; rami of the lower 

 jaw transverse, meeting, with teeth along its entire length; premaxillary large. 

 (Stegophilinw.) 

 i. Accessory caudal rays few, not conspicuous; caudal not fan-shaped nor exces- 

 sively contracted at base; upper lip with fine, hair-like, movable teeth. 

 j. Gill-membrane confluent with the isthmus; gill-openings reduced to a 

 narrow slit in front of the pectoral. 

 k. Opercle with two spines. VII. . .Henonemus Eigenmann & Ward. 

 kk. Opercle with four to twelve spines. 



1. Caudal deeply forked, the upper lobe prolonged; eight or nine 

 spines on the interopercle; color in bands; origin of ventrals 

 equidistant from caudal and angle of mouth. 



VIII. Pseudostegophilus Eigenmann & Eigenmann. 



U. Caudal emarginate or obliquely rounded, origin of ventrals 



nearly equidistant from snout and caudal; color, if present, in 



spots IX. Homodiastus Eigenmann & Ward. 



