ANNOTATED LIST OF THE SPECIES 157 
head 1.8; depth at origin of pectoral in length 9.7; distance from last anal ray to 
base of middle caudal rays (length of peduncle) in length 3.6—4.0 (mode about 3.7; 
in rivulatum of the same size mode about 4.4); depth of peduncle in length 10 
(6.8-8.0 in rivulatum). Contours gradually verging from depressed to com- 
pressed narrowly. 
Eye minute, slightly forward on head, nearly concealed; snout 2.5 in head; 
interorbital space 3.6 in head; barbels short; narial barbels 2.2-2.6 in the head; 
maxillary barbels 1.8—2.0 in head; inferior maxillaries 2.1—2.4 in the head. 
Longest pectoral rays 1.2—1.3 in the head; first pectoral rays not prolonged, 
and short as last; origin of dorsal equidistant from end of opercle and base of 
middle caudal rays, directly above end of ventrals; end of dorsal basis above middle 
of anal; anal the larger with few accessory rays; ventrals very small; accessory rays 
of caudal not greatly pronounced; caudal truncate to subtruncate. 
Color in alcohol generally a plumbeous gray, shading into yellowish on sides 
and about the pectoral fins; small, faint spots not uniform nor well localized, 
especially numerous in the young. 
The small, braided type-stream drains an extremely rugged and desolate 
country where it flows through a narrow canyon, its various small rami often dis- 
appearing beneath the rocky bed. At first impression the fishes were taken to be 
emaciated specimens of a form like taczanowskii, due to the nature of the stream. 
117. Pyaiprum KNERII (Steindachner) 
Trichomycterus knerii Steindachner, 1882, Denksch. Kk. Akad. Wiss. Wien, XLVI, 21, pl. v, figs. 
1-la, Canelos, Ecuador; 
non Kigenmann and Eigenmann, 1889, Proc. Cal. Acad. Sei., (2), I, 52: 
non Eigenmann and Eigenmann, 1890, Occ. Papers Cal. Acad. Sei., 1, 335. 
Trichomycterus kneri Boulenger, 1887, Proc. Zool. Soc. London, 278. 
Pygidium kneri Eigenmann, 1918, Mem. Carnegie Mus., VII, 314, pl. xlvi, figs. 1 and 2. 
Eastern Ecuador to Rio Meta 
Genus 56: PAREIODON Kner 
Pareiodon Kner, 1855, Sitab. KIX. Akad. Wiss. Wien, XVII, 160; 
Eigenmann and Eigenmann, 1890, Occ. Papers Cal. Acad. Sei., 1, 346; 
‘igenmann, 1910, Rept. Princeton Univ. Exped. Patagonia, III, 401; 
Eigenmann, 1918, Mem. Carnegie Mus., VII, 343. 
Centrophorus Kner, 1855, Denksch. Kix. Akad. Wiss. Wien, XVII, 161. 
Pariodon Giinther, 1864, Cat. Fish. Brit. Mus., V, 275. 
Type: Pareiodon microps Kner 
Amazon basin 
The gill-membranes confluent with the skin of the isthmus; the gill-opening a 
narrow slit; opercle and preopercle with numerous small spines; mouth nearly 
terminal; a single series of pointed incisors in each jaw; nasal and mental barbels 
wanting; double maxillary barbels at angles of mouth; anal short; caudal forked. 
