196 THOMAS SAY FOUNDATION 



ridge, pointed in the rear and with transverse grooves on 

 its ventral surface ; tergites normal, subanal lobes modi- 

 fied into broad triangular subgenital hooks which recurve 

 upon the tenth tergite. 



Female. Subgenital plate triangularly produced en- 

 tirely across ninth sternite, with a median notch. 



Distribution. — Type, female, No. 11328, Clayton, Geor- 

 gia, June, 1909 (Banks Coll., Mus. Comp. Zool., Cam- 

 bridge) ; Tallulah Falls, Georgia, June 17; North Carolina. 



Family NEMOURIDAE. 



This family is characterized by absence of long tails 

 in the adult forms. In Nemoura, Leuctra and Perlomyia 

 the tails or cerci are composed of a single segment which 

 in some instances is modified into an accessory copulatory 

 organ, while in Taeniopteryx the cerci vary, being com- 

 posed of single segments in some males, of several seg- 

 ments in others and in the female always made up of 3-10 

 segments. Insects mostly of a dull brown or blackish 

 color. Head usually a little wider than prothorax, with 

 long slender antennae; three small ocelli (except Taeni- 

 opteryx occidentalis Bks., which has only two) ; hind ocelli 

 closer to the eyes than to each other. First and third 

 tarsal segments subequal in length ; second either very 

 short or as long as the first ; second anal vein of f orewing 

 forked. 



The genitalia are mostly very complicated in the males. 



When better known this family, which is of wide dis- 

 tribution, will probably contain the largest number of 

 species of stoneflies. Superficially the species within a 

 genus look very much alike and it is only after thorough 

 relaxation or after boiling of the abdomen in caustic pot- 

 ash that the genital characters are brought out sufficient- 

 ly for specific determination. 



Key to the Genera of Nemouridae. 



1. Second tarsal segment about as long as the oth- 



ers; cerci of females composed of three or more 



segments, of males variable Taeniopteryx 



Second tarsal segment much shorter than the 

 others; cerci composed of a single segment 2 



2. An oblique crossvein in the apical marginal space 



beyond the tip of subcosta ; wings not rolled 



around the body when at rest Nemoura 



No crossvein beyond the tip of subcosta; wings 

 rolled around the body when at rest 3 



