[39] REVIEW OF THE SCIiENID^. 381 



This genus consists of fresh- water Scioenoids, inhabiting the rivers of 

 South America. The genus seems to us a valid one, although closely 

 allied to Corvula and Pseudotolithus, from both of which it is well dis- 

 tinguished by the peculiar squaination of the lateral line. This char- 

 acter suggested to Dr. Stein dachner the name Diplolepis, a name 

 which is, unfortunately, preoccupied. As no species of Plagioscion was 

 named by the describer of that genus, we have hesitated as to the 

 propriety of making use of that name. The original description of 

 Plagioscion must, however, certainly have been based on some species 

 of the present genus, as it agrees with no other American form. We 

 have therefore retained the name given by Dr. Gill in preference to 

 coining some new one for the group. 



Like most fresh- water fishes, the species of Plagioscion are subject to 

 many variations, especially in regard to the size of the second anal 

 spine. But three of the numerous nominal species seem to us valid. 



ANALYSIS OF SPECIES OF PLAGIOSCION. 



a. Second anal spine small, scarcely longer than eye, its length 4 to 5^ in head; teeth 

 of lower jaw with the inner series considerably enlarged; snout of moderate 

 length, 5 in head ; eye, 5£ ; maxillary, 2iin head ; gill-rakers rather long, X+12; 

 pseudobranchiae usually small on one side and obsolete on the other ; upper part 

 of the preopercle crenulate on its bouy margin ; pectoral fin short, If in head i 

 anal spine, 41 to 5J, its length subject to much variation ; caudal convex ; ven- 

 trals filamentous at tip. Color, silvery ; darker above, the ^il with a large 

 black spot. Head 3£ in length; depth 3£. D. X-I, 31 or 32. A. II, 7. Scales 

 (large ones or pores) 49 to 53. Lower pharyngeals narrow, armed with villiform 

 teeth Squamosissimus, 37. 



aa. Second anal spino large and strong, its length 2 to 3 in head. 

 b. [Teeth of lower jaw with the inner series considerably enlarged'; snout very 

 short, blunt, 5| in head ; head depressed above the eyes ; mouth large, rather ob- 

 lique, subinferior, the maxillary 2J in head, reaching past eye ; back elevated ; 

 ventral outline nearly straight ; caudal peduncle slender ; preorbital broad, a lit- 

 tle narrower than eye, which is 5£ in head; preopercle rounded, nearly or quite 

 entire ; teeth of outer series iu upper jaw and inner series of lower notably en- 

 larged ; dorsal spines slender, the highest 2f in head ; pectoral 1| in head ; ven- 

 trals If; scales all ctenoid; head 3| ; depth 3|; D. X-I, 31 to 33. A. II, 6. En- 

 larged scales in lateral line about 50 ; about 100 in a longitudinal series above it. 

 Color grayish above, silvery below ; upper vertical fins punctate ; lower fins yel- 

 lowish; axil dark.] {Steindacliner.) Surixamensis, 38. 



bb. Teeth of lower jaw subequal, those of the inner row scarcely enlarged ; head very 

 convex above, not spongy ; preopercle with a broad membranous margin, which is 

 slightly crenulate; preorbital broad, as broad as eye ; mouth large, oblique, the 

 lower jaw slightly included, the maxillary 2£ in head; snout bluntish, 3| in head, 

 eye 6 in head ; gill-rakers X + 13, slender and moderately long, the longest about 

 § diameter of eye; outer teeth above somewhat enlarged; pectorals loug, 1^ in 

 head, shorter than the ventrals, which have filamentous tips ; second anal spine 

 2j to 2f in head ; dorsals connected, the soft dorsal largely scaly at base ; caudal 

 rhombic, the middle rays produced. Color plain silvery, the axil dusky. Head 

 3£; depth 3J. D. X-I, 34 to 36. A. 11,7. Scales 49 (pores); 80 cross-series. 



Auratus, 39. 



