198 THOMAS SAY FOUNDATION 



Male. Supra-anal plate prolonged into a process, 

 which either recurves over the abdomen or is di- 

 rected upwards and backwards; subanal lobes either 

 simple or variously modified into accessory copulatory 

 organs; ninth abdominal sternite prolonged into a sub- 

 genital plate which bears (except in N. punctipennis) at the 

 base a flap-like appendage, the ventral lobe. 



Female. Seventh abdominal sternite either unmodi- 

 fied or produced over the eighth sternite in the 

 form of a subgenital plate ; genital opening of the eighth 

 sternite usually guarded by two valves. 



Genotype, Nemdura variegata Oliv. (Europe) . 



Under the genus Nemoura the European workers (Ris, 

 Kempny, Klapalek, et al.) recognize at least four sub- 

 genera: Protoiicmoura Kempny, Amphinemoura Ris, Nemoura 

 s. str. and Xcmouraclla Kempny. Although it may be pos- 

 sible to group the European species under these sub- 

 genera we have been unable to do so with the North 

 American forms, partly because some of the species do 

 not fit into any one of the subgenera, but particularly be- 

 cause the immature stages of only a few species are 

 known. Consequently they are here all placed under the 

 genus Xcmoura s. lat. 



Key to Species of Nemoura.* 



Males. 



0. Ninth abdominal sternite without a basal ven- 



tral lobe punctipennis 



Ninth abdominal sternite with a basal ventral 

 lobe 1 



1. Ninth tergite bearing two large rounded knobs__ 



stigmata 



Ninth tergite nearly smooth, without distinct 

 knobs 2 



2. Supra-anal process directed backward and up- 



ward but not recurved; subgenital plate long 

 and turned up at a right angle 3 



*N"ote. — Since the size, color markings, shape of prothorax, etc., vary 

 considerably in individuals of the same species, the genital structures 

 are used largely in differentiating the species. The genitalia of the 

 males are highly complex and furnish excellent specific characters, but 

 it is necessary in most cases to remove the abdomen and boil and clear 

 it in caustic potash in order that the different parts may be distin- 

 guished. Pinned specimens are almost hopeless for determination. The 

 genitalia of the females do not show such striking differences in the dif- 

 ferent species, and where species have not been reared it is not always 

 easy to connect the males and females properly. 



