EIGENMANN-i THE PYGIDIID-ffi, A FAMILY OF SOUTH AMERICAN CATFISHES. 289 



pectoral, but is usually shorter; no mental barbels; eye small, in the middle of the 

 head, or just in front of the middle, without a free orbital rim; interopercle with 

 numerous spines in several scries, those of the outer scries largest (in the very young 

 in a bunch as long as the opercular bunch, in the older in a much larger patch); 

 opercle with a bunch of similar spines; gill-membranes narrowly united with the 

 isthmus and usually with a narrow, free margin across it; mouth of moderate width, 

 terminal, the jaws with two or more series of chisel-shaped or conic teeth; no teeth 

 on lips or on the vomer; fins without spines, the pectoral short, the outer, simple 

 ray usually prolonged into a filament extending distinctly beyond the rays; ventrals 

 small, placed in the middle or considerably behind the middle of the body; anal 

 short, usually in part below, more rarely behind, the dorsal; caudal short, broadly 

 rounded, truncate or slightly emarginate, accessory rays variable, sometimes very 

 conspicuous, sometimes much less so ; origin of the dorsal between the vertical from 

 the origin of the ventrals and anal, always nearer the base of the caudal than to the 

 snout; the fin is low, rounded, short, with a variable number of rays up to twelve. 

 Cuvier & Valenciennes state that the first ray of the dorsal of .P. nigricans is pro- 

 longed in a filament. Is this a lapsus digiti for first ray of the pectoral? The 

 dorsal and anal have from two to four minute accessory rays entirely hidden in the 

 thick skin in front of the evident portion of these fins. 



The color may be uniform, or there may be one or three longitudinal stripes 

 or rows of spots, or large spots less regularly arranged, or numerous small spots 

 which may be discrete, or which may coalesce into vermiculations. There are no 

 distinct cross-bars. If the markings are longitudinally arranged, a series of spots 

 may be replaced by a stripe or vice versa in different individuals of the same species. 



Some of the species are of very small size, the maximum recorded size is 350 

 and 390 mm. in P. rivulatum and P. taczanowskii from Peru. 



The eggs reach 2.5 mm. in diameter. 



The species differ from each other largely in the shape of the teeth, the length 

 of the barbels, the relative position of the dorsal, anal, and ventrals, and in the 

 color. 



Distribution. — The members of the genus Pygidium belong particularly to the 

 mountains, where they live in all waters from small rills to large lakes like Titicaca. 

 They are frequently found under rocks or buried in the muddy banks of streams. 

 They extend from Panama southward to Chile and Patagonia, where they are 

 replaced by the members of the allied genus Hatcheria. In favorable places they 

 descend to the sea, as at Jequetepec and Callao, and they are among the last or are 

 the very last to disappear in ascending the mountains, where they are associated 



