150 FISHES OF WESTERN SOUTH AMERICA 
Eigenmann and Eigenmann, 1890, Oce. Papers Cal. Acad. Sci., I, 322. 
Pseudocetopsis ventralis EKigenmann, Rept. Princeton Univ. Exped. Patagonia, ITT, 398. 
Known only from Orton’s specimens at the Philadelphia Academy Museum. 
Subfamily: PYGIDIINAE 
Mostly or altogether free-living South American Nematognaths, having the 
dorsal fin over or behind the ventrals; adipose fin wanting; opercle and interopercle 
spinous; barbels reduced to a pair at each angle of the mouth, and otherwise irregu- 
lar; frequently of elongated, almost eel-like form, but very diverse in form and 
habit; generally intrusive, by virtue of the spines and hooks which anchor them to 
the sides of an opening, as they elbow themselves among the rocks of rapids and 
rifles or burrow in sand or mud, or insinuate themselves into the cavities and gill- 
chambers of other fishes. 
Fishes of the highlands and scantily dispersed into adjacent lowlands, rarely 
down to near sea-level. Next to Orestias the dominant fishes of the high Andes. 
Genus 54: PARIOLIUS Cope 
Pariolius Cope, 1871 (1872), Proc. Acad. Nat. Sci. Phila., XXTIT, 289; 
HKigenmann and Eigenmann, 1889, Proc. Cal. Acad. Sci., (2), II, 50; 
EFigenmann and Higenmann, 1890, Oce. Papers Cal. Acad. Sci., I, 324; 
Gosline, 1940, Copeia, no. 2, 78. 
Type: Pariolius armillatus Cope 
Range that of the species 
fan) 
Dorsal fin in front of the ventrals; no nasal barbels; opercle and preopercle 
without spines; a single barbel on each maxillary and two pairs of mentals. Near 
Pygidium, but not conforming to the boundaries of the subfamily; probably out of 
order here, and nearer the main trunk of the Stegophilines. Gosline considers 
it a nearer ally of the Pimelodidae. 
109. PARIOLIUS ARMILLATUS Cope 
Pariolius armillatus Cope, 1871 (1872), Proc. Acad. Nat. Sci. Phila., X XTIT, 289; 
Eigenmann and Eigenmann, 1890, Occ. Papers Cal. Acad. Sce1., I, 324; 
Eigenmann, 1910, Rept. Princeton Univ. Exped. Patagonia, IIT, 398; 
Gosline, 1940, Copeia, no. 2, 79. 
Rio Ambyiacu 
With new material from R. Ambyiacu Gosline has redescribed this fish. 
Genus 55: PYGIDIUM Meyen 
Trichomycterus Valenciennes, 1833, in Humboldt, Rec. d’Obs. Zool. Anat., H, 348, non Thricho- 
mycterus Humboldt. 
Pygidium Meyen, 1835, Reise in Peru, I, 474, fuscum; 
Eigenmann and Eigenmann, 1890, Oce. Papers Cal. Acad. Sci., I, 325; 
