160 FISHES OF WESTERN SOUTH AMERICA 
Eigenmann, 1910, Rept. Princeton Univ. Exped. Patagonia, III, 401; 
Eigenmann, 1918, Mem. Carnegie Mus., VII, 355, fig. 28. 
Rio Huallaga 
Liitken considers this species as an intermediate between the Stegophilines 
and Pygidium. 
Genus 60: APOMATOCEROS Eigenmann 
Apomatoceros Eigenmann, 1922, Bijd. Tot de Dierk., X XII, 113, pls. iii and iv, figs. 1-9. 
Type: Apomatoceros alleni Eigenmann 
Peruvian Amazons 
Near Acanthopoma, but lacking the opercular spines; caudal furecate; upper 
jaw widened so as to enclose the short, narrow, lower jaw; gill-membranes united 
with the isthmus, except for a broad, free membrane. 
123. APOMATOCEROS ALLENI Eigenmann 
Apomatoceros allent Figenmann, 1922, Bijdr. Tot de Dierk., XXII, 118, pls. i and iv, figs. 1-9. 
Rio Morona and Maranon 
First taken on the extreme border of the Amazonian flood plain within view 
of the foothills of the Andes. Dr. G. 8. Myers (letter) states that it has been re- 
discovered far down the Maranon at Pebas, by Mr. Wm. G. Scherer. 
15500, 1, 146 mm., type, Rio Morona, Allen, October, 1920. 
H. 8; depth 9; depth of head 16; eye 5.33 in head; interorbital equals snout 
plus half the eye diameter; P. 11 in the length; upper caudal lobe equals head, 
lower slightly longer. Depth of caudal peduncle 2.4 in its length. D. 9; A. 8; 
base of anal nearly double that of dorsal; compressed behind pectorals, greatly 
compressed forward, pectorals nearly horizontal. 
Mouth very large, subcircular, upper jaw flexible, curling inward, prolonged 
backward to near tips of interopercular spines; terminal barbel of the maxillary 
reaching tips of interopercular spines, lower barbel very small, scale-like in shape; 
lower jaw firm, not reaching forward to middle of eye; upper jaw evidently elastic 
and expansible into a disk for attachment. Seven very regularly arranged, con- 
centric series of teeth in upper jaw; shorter rows interpolated between these near 
the symphysis to a total of eleven, the number of rows decreasing to four at the 
end of the premaxillary, only the outer four rows continued across the middle, 
the others interrupted in the middle by a naked area; four rows of similar teeth in 
the lower jaw, those of the two rami separated by a considerable space free of teeth. 
Gill-membranes united and joined to the isthmus, but with a wide, free membrane 
across the isthmus. Distance between the anterior nares more than twice the 
distance between the posterior. A median, dermal keel from the base of the last 
ventral ray to between the tips of the pectorals. Interopercle with a series of five 
straight spines; opercular spines wanting. 
