36 ZOOLOGY. 
a great 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 greyish 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 Basilichthys 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 SILURIDZ. 
= Genus NEMATOGENYS, Girard. 
Gen. car. 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. 
Syn. Nematogenys, Grp. Proc. Acad. Nat. Sc. Philad. VII, 1854, 198. 
Ons. The most prominent characters by which this genus may be distinguished from Thricho- 
mycterus, 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. 
Pirate XXXII, Figs. 1—3. 
Spec. car. 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. 
Vematogenys inermis, GRD. Proc. Acad. Nat. Sc. Philad. VII, 1854, 198. 
Bagre or Vagre. Vernacular. 
