II 



UULLETINT 36, UNITED STATES NATIONAL MUSEUM. 



(liiniuislied by the fact that the specimen of S. brasilicnsis is very young. 

 The characters drawn oat by M. Eil. Van Beueden are as follows : 



Characters. 



1. Size 



2. Kumber of vertebra" 



3. Kumber of ribs (pairs) 



4. Number of sternal ribs (pairs) 



5. Number of pieces in sternum . 



C. Number of teetb 



7. Ear-bones 



S. guianensis. 



greater. 

 55 

 12 



7 



29 

 smaller. 



S. brasiliensis. 



smaller. 



54 



11 



G 



^1 (of bone); 



(1 (of cartilage). 



31 



33 

 f lar g e r and 

 ( peculiar. 



On account of the immature condition of the specimen o^S. hrasiUensis, 

 characters 1 and 5 are manifestly of little importance. The differences 

 represented in characters 2, 3, and G are within the range of individual 

 variation, as has been abundantly proved by the examination of various 

 species. Characters 4 and 7, therefore — the number of sternal ribs and 

 the size and form of the ear-bones— alone constitute recognizable dis- 

 tinctions between the two species, Of these two characters, the first is 

 quite likely to be merely an individual difference j but the second can 

 not of course be so considered. 



Between S.fluvlatiUs and S. pallida, the following distinctions are 

 made: 



Color— 



S. flaviatiUs : Body black above, rose-piuk below ; pectorals colored like tbo back. 



S. pallida : Body fulvous above, white below ; pectorals uofc colored like the back. 

 Pectoral lius — 



S. fliiviaiilis : Quite largo and pointed. 



S. pallida : Smaller, less pointed, and narrower at the base. 

 Dorsal fin — 



S. Jluvialilis : Two-tbirds as bigb as long. 



S. pallida : Less high. 



These distinctions are unsatisfactory, but can not be set aside without 

 reason. 



Between the five species we have but two points of comparison, the 

 color of the body and the number of teeth. The data given by the dif- 

 ferent original describers are as follows: 



S. hrasiliotsis — 



Color: Back blackish, sides fulvous, belly wliite; pectoral like the back. 



Teeth: 3 ;5. (E. Van Beueden.) 

 S. guianensis — 



Teeth: f|. (E. Van Beueden.) 

 S. lucuxi — 



Color: Darkish black or fuscous. Teeth: 3[!. (Gray.) 

 S.Jluviatilis — 



Color: Above black, beneath rose-color; pectorals like the back. (Gervais.) 

 S. pallida — 



Color: Above fulvous, beneath white; pectorals like the belly. Tectli : 3?- 

 (Gervais.) 



