FISH. 111 
itself is twice the length of that fin; very low at first, but gradually rising, until, before its 
termination, it becomes equal to between one-half and one-third of the depth. The vent is in 
the middle of the entire length, caudal excluded. Anal short, and just beneath the middle of 
the adipose, there being about one-fourth of this last fin in advance of it as well as behind it: 
the first four rays simple, but apparently all articulated, the first two or three very minute and 
not easily observed. Caudal forked for two-thirds of its length: the upper lobe a little longer 
than the lower, and contained five and a half times in the entire length. Ventrals imme- 
diately beneath the last ray of the dorsal; a little shorter than the pectorals, and not reaching 
to the anal by half their own length. 
DIVG= TAL 14% or 15" C i ee. PS 1/9 Vs G: 
Length 5 inches 2 lines. 
Cotour—(Jn spirits.) Brownish, inclining to silvery in some places: a dusky fascia formed of 
dots along the lateral line. Dorsal rather dusky at the base, and with the upper portion also 
dusky between the rays: a dusky spot on the anterior part of the adipose. 
Habitat, Rio de Janeiro. 
This species was taken by Mr. Darwin in a running brook at Rio de Janiero. 
It approaches on the whole so nearly the P. gracilis of D’Orbigny, that I can 
hardly suppose it to be distinct. Yet there are some slight differences observ- 
able in this specimen. It has more anal rays; the adipose appears shorter; and 
the upper lobe of the caudal is not so prolonged, though possibly it may be worn 
down. Also D’Orbigny’s figure appears to want the dusky stains on the dorsal 
and adipose fins. If it be not that species it must be new, as there is none other 
described by Cuvier and Valenciennes with which it will assimilate better. 
2. PIMELODUS EXSUDANS. Jen. 
P.. corpore parum elongato, altitudine quintam partem longitudinis equante: galed 
levi, inconspicud, processu interparietali haud clypeum parvum preédorsalem attin- 
gente: poris paucis buccalibus amplis, serie obliqua dispositis : maxillis equalibus : 
cirris sex; maxillaribus haud analem attingentibus: lined laterali primum deflexa, 
deinde rectd : pinnis dorsali et anali brevibus ; adiposd dorsali haud duplo longiore : 
caudali profunde bifurcd, lobis equalibus: spind pectorali margine interno fortiter 
dentato. 
Dein Ae lSivel 14: Oe 7s &eo3 P- 1/83) V6: 
Lone. unc. 3. lin. 6. 
Form.—In some respects resembling the last species, but the body much less elongated, the depth 
and thickness remaining the same. The depth is about one-fifth of the entire length; the 
head rather more than one-fifth. The helmet is scarcely so much wrinkled, and the inter- 
parietal process not so long, reaching only half-way to the buckler, which last is smaller and 
less obvious. The solution of continuity of the bones of the cranium appears to extend back 
