Cockerell: Scales of Characinid Fishes, 101 



Tetragonopterin.e. 

 A very large subfamily, of which numerous species have been 



studied. 



Phenacogaster megalostictns Eigenmann. Very broad scales, about 

 three and one-half mm. broad and only two and one-fourth mm. 

 long. They have basal and lateral circuli, the latter widely spaced; 

 apical field with rather strong growth-ridges, but no circuli; a few 

 (2 to 4 or 5) widely spaced, weak radii. This scale has no resem- 

 blance to that of the Bryconinae (Brycon and Holobrycon), but is 

 like that of Cheirodon. 



Deuterodon pinnatus Eigenmann. Small scales of entirely the same 

 type as the last, but only moderately broad, length about 1.5, 

 breadth 2 mm. or a fraction over. The radii vary from about 4 

 to 7. The nuclear field, which is subbasal, is microscopically reticu- 

 late, this pattern being derived from modified circuli. Exactly the 

 same reticulation may be seen in the scales of Phenacogaster megalo- 

 stictus, but it is not always very distinct. 



Astyanax Baird & Girard is a very large genus, divisible into Astyanax 

 proper and Pcecilurichthys Gill. The species examined are placed 

 under these headings. 



I. Pcecilurichthys. 



Asty nax polylepis (Giinther). Small scales, broader than long, with 

 rounded outlines, and evident, though broadly rounded, laterobasal 

 angles; circuli basal and lateral, the latter widely spaced; nuclear 

 area broad, with microscopic reticulations as in Deuterodon; apical 

 field with six or seven widely spaced radii, and no regular circuli, 

 but the compound microscope shows numerous broken rudiments, 

 slanting toward the middle line. This is certainly close to Deuter- 

 odon. 



Astyanax ahramoides Eigenmann. Scales not unlike those of A. 

 polylepis, but the circuli are more dense and regular, the radii are 

 about four, and the apical field is fully covered with circuli, which 

 meet at a very broad angle in the middle line. The nuclear rectiula- 

 tion is very irregular, and quite distinctive. 



Astyanax bimaculatus (Linnaeus) (Plate XXVI, fig. 7). Scales large 

 and thick, about six mm. long and seven and one-half mm. broad; 

 nucleus very little below the middle, with a minute labyrinthine 

 sculpture, derived from the circuli; circuli extremely fine and dense, 



/m^^^ 



nS /s, 



