FISH. 3 
No true perch had been obtained from South America until M. D’Orbigny 
discovered one in the Rio-Negro, in North Patagonia, which has been since de- 
scribed by Valenciennes, under the name of P. trucha.* The present species 
was found dead by Mr. Darwin, high up the river of Santa Cruz, in South 
Patagonia. It is evidently very closely allied to the P. trucha, and is spotted in 
a similar manner; but it appears to differ in the scales not advancing on the 
snout beyond the nostrils, or covering more than the posterior half of the subor- 
bitals. Those on the body are also particularly characterized by being so smooth, 
as hardly to communicate any sensation of roughness when the hand is passed 
from the tail towards the head, though the head itself is rough. This circum- 
stance has suggested the specific name. This species further disagrees with the 
one above alluded to in having the caudal slightly forked, not rounded; and in 
having two soft rays less in the second dorsal, and one less in the anal. Valen- 
ciennes’s description, however, of the P. érucha is very brief; on which account 
I have been the more minute in that of the P. levis. 
This perch, with P. trucha, would almost seem to form a subordinate division 
in the genus, distinguished from that embracing all the other described species, 
by the character of the scales covering a large portion of the head which gives it 
a remarkable scienoid appearance. Both species may be known from all the 
North American perches, by their having the body spotted instead of banded, 
and by the smaller number of rays in the first dorsal. In this last character they 
agree with the P. ciliata, and P. marginata of Cuvier and Valenciennes. 
1. SERRANUS ALBO-MACULATUS. Jen. 
Puate II. 
S. lateribus maculis albis serie longitudinali dispositis ; dentibus velutinis ; paucis, hic 
et illic sparsis, fortioribus, aculeiformibus, vel sub-conicis ; preoperculo margine ad- 
scendenti convextusculo, denticulato ; denticulis ad et infra angulum pauld majoribus ; 
operculo mucronibus duobus parvis, et spind intermedia forti, armato ; rostro et max- 
allis nudis ; squamis corporis leviter ciliatis ; pinnd caudali equali. 
B.7s Di1OtSss AC 3/7 C.17&e.— P72 V. Wd. 
Lone. unc. 16; lin. 9. 
Form.—Of an oblong-oval form, with the greatest depth about one-fourth of the entire length. 
The dorsal and ventral lines are of nearly equal curvature. The profile is nearly rectilineal, 
* Hist. des Poiss, tom. ix. p. 317. I refer to the quarto edition throughout. 
