FISH. 



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. trueka* 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. trucha is very brief; on which account 

 I have been the more minute in that of the P. Icevis. 



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 scisenoid 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. 



Plate II. 



S. lateribus maculis albis serie longitudinali disposilis ; denlibus velutinis ; paucis, hie 

 el iliic spar sis, for tioribus, aculeiformibus, vel sub-conicis ; preoperculo margine ad- 

 scendenti convexiusculo, denticulato; denticulis ad et infra unguium pauld majoribus; 

 operculo mucronibus duobus parvis, et spina intermedia for ti, armato ; rosiro et max- 

 illis nudis ; squamis corporis leviter ciliatis ; pinna caudali asquali. 



B. 7; D. 10/13; A. 3/7; C. 17, &C.-P. 17; V. 1/5. 



Long. 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. torn. ix. p. 317. I refer to the quarto edition throughout. 



