242 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. 



Br. XII; D 10; A 11; C 16. I. 1. 1. I. 12; V 6; P I. 7. 



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 Eio 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 ine)-mis 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.) Valenc. 



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. Eyes 

 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. 



Syn. Thrichmnydcrus (Humb.), Valenc. in Humh. Rec. d'Obs. de Zool. et d'Anat. comp. II, 

 1833, 347. 

 Cuv. et Val. Hist. Nat. Poiss. XVIII, 1840, 485. 

 GuicH. in Gay, Hist, de Chile, Zool. II, 1848, 309. 

 GiRARD, in Proc. Acad. Nat. Sc. Philad. VI, 1854, 198. 



