152 Proceedings of the Biological Society of Washington. 



4. Scales very broad and short, with very few radii ; circuli absent in 



apical field 5. 



Scales longer than broad, or if broader than long, not excessively so . 6. 



5. Circuli extremely dense, essentially transverse (Clupeidse) 



Opisthopterus dovii Giinther. (Panama market.) 

 Circuli not dense, concentric (Hemiramphidy?) 



Hyporhamphus unifasciatus Ranzani. (Balboa.) 



6. Small scales, with rounded laterobasal corners, and numerous radii . 7. 

 Larger scales, with angular or subangular laterobasal corners, or if 



(Gastropelecus) sometimes rounded, then radii very few .... 9. 



7. Lateral and apical circuli crossed by fine radial lines of hyaline dots 



(Pleuronectidae) . . Citharichthys spilopterus Giinther. 



lower side (Toro Point. ) 

 No such lines of hyaline dots 8. 



8. Radii (all basal) less than ten (Pleuronectidae) 



Paralichthys woolmani Jordan & Williams, 

 upper and lower sides (Taboga I.] 

 Radii extremely numerous ; circuli in apical field broken up ( Dacty- 

 loscopidse) Dactylagnus mundus GiU. (Taboga I.) 



9. Radii few, mostly apical ; or when many basal, central region of scales 



with coarse radial reticulation (Characidse) 10. 



Radii numerous, all apical ; basal margin not lobed (Characidse) . 11 . 

 Radii apical and basal ; basal margin deeply lobed ; center of scale 



not reticulated (Characidse) . Curimatus magdaleneeSteindachner 



(Rio Abaco.) 

 Radii basal 12. 



10. Circuli absent in apical field ; centre of scale with a minute reticula- 



tion derived from the circuli 



Gastropelecus maculatus Steindachner. (Creek near Chorera. ) 

 Circuli broken up, but coarse and conspicuous, in apical field; some 

 scales with a central reticulate pattern derived from the radii 



Piabucina panamensis Gill. ( Rio Calobre. ) 



11. Circuli represented in apical field by a broken zigzag pattern 



^sJyanax^sc^m Steindachner. (Creek near Chorera.) 

 Circuli not showing a zigzag pattern in apical field 



Astyanax grandis Meek & Hildebrand. (Rio Abaco. ) 



12. Scales longer than broad, with only three or four radii, in deep folds; 



basal margin lobed ( Synodontidse) 



/Si/nodus evermanm Jordan & Bollman. (Taboga I.) 

 Scales broader than long 13. 



13. Radii 6 to 8; basal margin strongly crenulate (Xystsematidse) 



Oerres rhombeus C. & V. (Mindi Cut. ) 



Radii more than ten ; basal margin without regular crenulations 



(Poeciliidse) 14. 



14. Circuli obtusely angulate in median line above nucleus 



Pcecilia sphenops C. & V. (Corazal.) 



