772 



THE AMERICAN NATURALIST [A^ol. XLI 



and post-ventral regions are trenchant. In Stethaprion, Brachy- 

 chalcinus and Fowlerina the post-ventral region is incipiently 

 serrate and there is a pre-dorsal spine. In Mylesinus of the 

 Myleinae the abdomen is serrate behind the ventrals and in the 

 rest of the IMyleinae and the Serrasalminae the ventral edge is 

 serrate both in front and behind the ventrals. The descent is 

 indicated as follows 



Tetragonopterus 



I 



Stichonodon 



Stethaprion — Fowlerina — Brachychalcinus 



I 



I\Iylesinus 

 1 I 

 other Myleinae Serrasalminae. 

 The genera of Stethaprioninae are distinguished as follows. 

 a. No predorsal spine; caudal scaled; origin of anal posterior 



to dorsal Stichonodon. 



aa. A predorsal spine. 



b. Predorsal spine long, slender, spear-shaped, fitting into 

 a groove in the back; origin of anal under dorsal; scales 

 rather small, over 60 in the lateral line. 



Stethaprion. 



bb. Predorsal spine scale-like, spoon or saddle-shaped, 

 concave below, fitting into a notch in the back. Caudal 



scaled; scales less than 40 Fowlerina. 



bbb. Predorsal spine trigger or hammer-shaped, its free 

 portion forming a longer anterior and shorter posterior 

 branch, both of which are sharply pointed; caudal scaled; 

 scales large, about 40. ... Brachychalcinus. 

 University of Indiana, 

 Bloomington, Ind. 



