38 ZOOLOGY. 
their anterior edge being placed a little in advance of the posterior expansion of the opercle. 
The spine which occupies this region is well developed, provided with minute prickles beneath, 
and with a series of small, subtriangular serratures posteriorly. Its tip is continued to the 
margin of the fin under the form of a membranous ray. The soft and articulated rays are bifur- 
cated three times. The external margin of these fins is rounded when expanded. 
Bree DO) Ae Cal Ge al Note Lalli Valo eae 
The anterior ray of both the dorsal and anal fins is small and slender, and the second shorter 
than the third, which is a little longer than the last of all. 
The skin is densely studded with minute pustules, smooth to the touch, and extending to all 
the regions, except the lower surface of the head, throat, and belly. The lateral line, from 
the opercular apparatus, runs almost straight along the middle of the flanks to the base of cau- 
dal fin, undergoing but a very slight inflexion downwards upon the thoracic region. It is much 
more conspicuous anterior to the dorsal fin than farther back, where it exists under the shape 
of small pores. 
The ground-color is reddish, or yellowish brown. The upper surface of head is nearly black ; 
numerous blackish and rounded spots or blotches are spread all over the body and sides of the 
head, with a tendency towards longitudinal series along the flanks and tail ; the blotches often 
being confluent, and inconspicuously defined. On the fins, these spots assume a transverse 
arrangement, and give to the latter an irregularly banded or barred appearance. The inferior 
surface of the head and belly are whitish, the former regions sometimes maculated. The buccal 
and prenasal barbels are black; the subhyoidal ones whitish, or semi-blackish. The ventrals 
and pectorals are lighter beneath than above. 
Specimens of this species were collected in an affluent of the Rio de Maypu, in the vicinity of 
Santiago. According to Mr. Gay, it is to be found in the fresh waters throughout the republic 
of Chile. - 
Plate XXXII, fig. 1, represents Nematogenys inermis in a profile view, and nearly the size of life. 
fig. 2, is an outline of the fish seen from above, to show the disposition of 
the eyes, nostrils, and prenasal barbels. 
fig. 3, is a view of the inferior surface of the head, exhibiting the insertion 
of the subhyoidal barbels, the continuity of the branchial aperture with the 
hyoidal apparatus, and the branchiostegal rays. 
Genus THRICHOMYCTERUS, (Humb.) Valence. 
Gen. cHAR. Head depressed and rather small. Body anteriorly rounded ; posteriorly com- 
pressed. Caudal fin emarginated or subemarginated. Anal under the posterior part of dorsal, 
and ventrals in advance of the latter. Mouth small, or of medium size, inferior, and provided 
with a double pair of barbels at its angle. No barbels under the head. One pair of prenasal 
barbels. Velvet-like teeth upon the intermaxillaries and lower jaw. Palate smooth. Hyes 
very small, situated on the upper surface of the head. Opercular apparatus prickly. Branchial 
openings not continuous under the throat. Fins without any spiny rays. Skin scaleless and 
smooth. 
Syy. Vhrichomycterus (Humb.), Vatenc. in Humb. Rec. d’ Obs. de Zool. et d@ Anat. comp. IT, 
1833, 347. 
Cuy. et Van. Hist. Nat. Poiss. X VIII, 1846, 485. 
GurcH. in Gay, Hist. de Chile, Zool. II, 1848, 309. 
GrrRaARD, in Proc. Acad. Nat. Sc. Philad. VI, 1854, 198. 
