110 ZOOLOGY OF THE VOYAGE OF THE BEAGLE. 
MALACOPTERYGII. 
Famity. SILURIDZ. 
1. Pimetopus cGraciuis. Val. 
Pimelodus gracilis, Va/. in D’Orb. Voy. dans |’ Amer. Mérid. Atl. Ichth, Pl. 2. fig. 5. 
———_———__ Cuv. et Val. Hist. des Poiss. tom. xv. p. 134. 
Form.—Of a slender elongated form, the body compressed behind the dorsal. Greatest depth con- 
tained about seven and a half times in the entire length: thickness at the commencement of 
the dorsal a little less than the depth. Head, measured to the gill-opening, rather more than 
one-sixth of the entire length: its breadth two-thirds of its own length. Helmet smooth, and 
not very conspicuous, though with its whole surface finely wrinkled: its breadth behind the 
eyes rather more than one-third of its length, measuring this last from the end of the snout to 
the further extremity of the interparietal process. The solution of continuity extends back 
nearly to the base of the process just mentioned,which last is narrow and lanceolate, three 
times as long as broad at its base, but not reaching to the buckler, or triangular plate in front 
of the dorsal, by one-third of its own length, The buckler itself is not very large, but sufti- 
ciently obvious. 
Profile sloping gradually downwards in nearly a straight line from the beginning of the 
dorsal to the end of the snout: this last depressed and rounded horizontally in the form of a 
semicircle. Mouth wide, but very little cleft, the commissure not reaching half way to the 
eye. Upper jaw projecting a very little beyond the lower. In each a band of very fine 
velutine teeth; but none on the vomer or palatines. ‘Tongue smooth, and fastened down all 
round. Six barbules; the maxillary pair very long, reaching to the commencement of the 
anal fin; of the submandibular pairs, the exterior reach one-third beyond the insertion of the 
pectorals ; the interior are only half the length of the exterior. Eyes round, of moderate size, 
their diameter four and a half times in the length of the head, situate in about the middle 
of the length: distance from one to the other one diameter and a quarter. Lateral line 
nearly straight throughout its course, dividing the body longitudinally into two nearly equal 
portions. 
Pectorals not quite equalling the length of the head, and a little less than one-sixth of the 
entire length : the spine very little shorter than the soft rays, very strong, with sharp teeth on 
its inner edge, but the outer edge only granulated, or with a few slight serratures towards the 
extremity. The humeral bone seen above the pectoral projects backwards in the form of a 
spinous lamina, but does not appear through the skin; it equals half the length of the pectoral 
itself. The dorsal commences at one-fourth of the entire length, and is of a somewhat rectan- 
gular form, the soft rays not decreasing much backwards: its length equals four-fifths of the 
depth of the body, and two-thirds of its own height. The spine is not so strong as that of the 
pectoral, and with only a few small serratures on the outer edge near the tip. The space 
between the dorsal and the adipose a little exceeds the length of the former. The adipose 
