The May-flies and Stone-flies 73 



straying far away. They rest on trees and bushes along the banks. The 

 green ones usually keep to the green foliage, while the dark ones perch on 

 the trunk and branches. The various species are included in ten genera, 

 which may be determined by the following table: 



TABLE OF NORTH AMERICAN GENERA OF PLECOPTERA. 



The following technical terms not heretofore defined are used in this key: cerci, 

 slender processes projecting from the tip of the abdomen; radial sector, cubital vein, 

 and other names of veins in the wings may be understood by reference to Fig. 109. 



P.A 



FIG. 109. Diagram of venation of wing of a stone-fly; I, costal vein; 2, subcostal vein; 

 j, radial vein; 4, medial vein; 5, first anal vein; 6, radial sector; P, pterostigma; 

 A, arculus: a,, a 2 , a z , apical cells. Between the medial and first anal vein is the 

 cubital vein, not numbered. Cell M is the cell behind the medial vein; cell Sc is the 

 cell behind the subcostal vein. 



A. With two long, many-jointed cerci. 



B. Radial sector not reduced, i.e., with four or more branches. 



C. Wings strengthened throughout by many cross-veins, there being many 

 cross-veins between the branches of the media, between the accessory 

 cubital veins, and in the anal areas of both pairs of wings. .PTERONARCYS. 

 CC. Wings with few or no cross-veins between the branches of the media, 

 between the branches of the cubital veins, and in the anal area. 

 D. Radial area of the fore wings with an irregular network of veins- 



DlCTYOPTERYX. 



DD. Radial area of the fore wing with no cross-veins except the radial 

 cross-veins, or with a few regular cross-veins. .. .PERLA (in part). 

 BB. Radial sector reduced, i.e., with less than four branches. 

 C. Hind wings much broader than the fore wings. 



D. With several cross-veins in cell M of the fore wings. 



E. Cell Sc of the fore wings with at least three cross-veins. 



F. With three ocelli PERLA (in part). 



FF. With only two ocelli PSEUDOPERLA. 



EE. Cell Sc of the fore wings with only one or two cross-veins. 



Small species of a green or yellow color CHLOROPERLA. 



DD. With only one cross-vein in cell M of the fore wings between the 



arculus and the medio-cubital cross-vein CAPNIA. 



CC. Hind wings of the same width as the fore wings; the anal area of the 



hind wings not expanded ISOPTERYX. 



AA. With the cerci rudimentary or wanting. 



B. Second segment of the tarsi equal in length to the others; rudimentary cerci 

 present T^ENIOPTERYX. 



