240 ZOOLOGY. 



a o-reat accumulation of dots over the whole surface of the scales, whilst beneath it there is but 

 one series of these dots along the very margin of the scales. The caudal, dorsal, and pectoral 

 fins are grej'ish yellow; the ventrals and anal are yellowish. The upper surface of head and 

 snout being dark brown. 



This species, which is said to inhabit the fresh waters of Chile, was caught by Mr. Darwin in 

 the vicinity of Valparaiso. The specimens before us were collected by Lieut. Gilliss in the 

 Mapocho, an affluent of the Rio de Maypu. 



Plate XXX, fig. 6, represents BasilicJdhys microlepidotus in a profile view, and of the size of 

 life, 

 fig. 7 is an outline, viewed from above, 

 fig. 8, a scale of the dorsal region, 

 fig. 9, a scale of the abdominal region. 

 Figs. 8 and 9 are magnified. 



FAMILY OF SILURID^. 



Genus NEMATOGENYS, Girard. 



Gen. CHAR. Head very much depressed and large. Body posteriorly compressed; posterior 

 margin of caudal fin rounded. Anal opposite space between the dorsal and caudal. Ventrals 

 under the dorsal. Mouth broad, but not deeply cleft ; its angle provided with a long barbel. 

 A second pair of subhyoidal barbels shorter than the buccal ones. A still shorter and prenasal 

 barbels constitute a third pair of these appendages. Intermaxillaries and dentaries provided 

 with a patch of card-like teeth. Pharyngobranchials covered with similar asperities. Eyes 

 rather small, situated on the upper surface of head. Opercular apparatus without any spines. 

 Branchial openings continuous under the throat. A spine at the anterior margin of the pec- 

 toral fins. Skin scaleless. 



Stn. Nematogenys, Grd. Proc. Acad. Nat. Sc. Philad. VII, 1854, 198. 



Obs. The most prominent characters by which this genus may be distinguished from TJiricJio- 

 myderus, consist in the presence of one pair of barbels only at the angle of the mouth, another 

 pair under the head, which is wanting in the latter, and by the absence of prickly or small 

 spines on the opercular apparatus. The absence of an isthmus under the throat may become 

 another not less important point of discrimination between the two genera. 



NEMATOGENYS INERMIS, Girard. 

 Plate XXXII, Figs. 1—3. 



Spec. CHAR. Head large and wedge-shaped: snout anteriorly broad and rounded. Origin of 

 ventrals opposite the anterior margin of dorsal. Spiny ray of pectorals prickly beneath. Tip 

 of buccal barbel extending beyond the base of pectorals. Skin beset with minute pustules. 

 Ground-color yellowish brown maculated with white. 



Syn. Trichomycterus inermis, GuiCH. in Gay, Hist, de Chile, Zool. II, 1848, 312. Ictiol. 

 Lam. ix, fig. 2. 

 Nematogenys inermis, Grd. Proc. Acad. Nat. Sc. Philad. VII, 1854, 198. 

 Bagre or Vagre. Vernacular. 



