1878.] 675 [Cope 
premaxillary border. The eye’s diameter is just half the interorbital 
width. The maxillary barbels exceed the length of the fish; and the pos- 
terior mandibulars reach to a point below the middle of the dorsal fin. 
Radial formula ; D. I. 6; A. 9. Dorsal spine very slender, smooth, and 
not so long as the pectoral spine. The latter is as long as from the pre- 
maxillary border to the middle of the orbit ; it is finely serrate on both edges. 
Operculum roughened with radiating lines ; supraocciptal process six times 
as long as wide. Total length M. .070, interorbital width .007; length of 
base of rayed dorsal .008. Color uniform plumbeous. 
Collection of 1877 ; two specimens. 
11. PIMELODUS OPHTHALMICUS, sp. nov. 
Head covered with a thin skin above which is involved in osseous wrin- 
kles on the post frontal region. Supraoccipital process four times as long 
as wide, reaching the basal bone of the dorsal spine. Length of adipose 
fin contained 2.8 times in the length minus the caudal fin. Form quite 
slender ; the greatest depth (which is at the middle of the dorsal fin) 
entering the length (minus the caudal) 6.5 times. The length of the head 
enters the same 4.75 times. The maxillary barbels reach to the middle of 
the anal fin, and the posterior mentals to the middle of the pectoral fin. 
The eye is large, entering the length of the head three and three-eighth 
times, and exceeding tle interorbital width by 2mm. The upper lip pro- 
jects a little beyond the lower. The two dorsal fins are separated by a 
space about equal to three-fourths the base of the anterior fin. The latter 
is higher than the depth of the body, and nearly equal to the length of the 
head ; the spine is slender, and finely dentate on both edges. The pectoral 
spine is finely serrate on both edges and is nearly five-sevenths the length 
of the head. Radial formula ; D.I. 6; A. 18; V.6; P. I. 8. Humeral pro- 
cess extending to middle of pectorai spines, striate grooved. Axillary pore 
present. Color brown lead-color ; top of head blackish ; dorsal fin brown 
at base, then clear, then blackish. Total length M. .145. : 
Coll. of 1873. 
This species belongs to the group with Pimelodus cristatus, P. elongatus, 
P. agassiztt, P. wesselii, etc. It appears to approach most nearly the first 
named, but that fish has, according to the descriptions, fifteen anal rays, 
and the mental barbels extend beyond the extremity of the pectoral fins. 
Giinther also states that its dorsal fin is nearly twice as high as long, which 
is not the case in my specimen, and the dorsal spine is not so long in the 
latter, being only three-fourths as long as the head instead of equal to 
it. The Pimelodus cyanostigma (Rhamdia cyanostigma Cope, Proceed. 
Amer. Philos. Soc. 1870, p. 569) is an allied species ; but it has a shorter 
adipose fin, which enters the length three and one-fourth times, and which 
is separated from the rayed dorsal by a space equal to the length of the , 
latter. Its maxillary barbels are also longer, extending to the end of the 
adipose fin. 
12. PimELopus BUFONIUS Cuv. Val. 
Coll. 1878-1877. 
