268 NEARCTIC ERYTHRONEURA (hOMOPTERA) 



the apical margin and the second apical cell is oblong and based 

 on a cross-vein. In Typhlocyha the fourth apical vein is curved, 

 terminating in radial margin, and the second apical cell is tri- 

 angular, sometimes even stalked. In the identification of species 

 the character of the fourth apical cell, the shape of vertex and 

 the color pattern appear to be the most important external char- 

 acters. The differences between groups are more or less bridged 

 by fluctuations in this extremely variable genus. On this ac- 

 count it may be necessary to run some specimens through the 

 keys of both Groups 4 and 5 as subsequently defined. The spec- 

 ies are not numerous, and as aggregates are easily recognizable 

 after a little experience, but variation is so great that it is diffi- 

 cult if not impossible to construct a synopsis, subject to so few 

 exceptions, that identification of chance individuals will be easy 

 and certain. Numerous new varieties are named in the present 

 paper, and the policy governing such naming will be only briefly 

 expressed here.^ Insects have varieties, different from the sub- 

 species of ornithology and mammalogy that seem to require re- 

 cognition in nomenclature; they have others which should not be 

 named. Conspicuous examples of the latter type or mere color 

 phases, are the varying red to yellow forms of Erythroneura. 

 Where the color pattern is the same but a transition in color oc- 

 curs, as from yellow to red, or from red to black, I have endeav- 

 ored to avoid nomenclatorial recognition of the variants. How- 

 ever where the color pattern differs, in shape, notably in extent, 

 or otherwise in any essential way the variety has been named. 

 The writer believes the accumulation of knowledge relating to 

 these varieties will ])e retarded if not prevented, l^y lack of means 

 of referring to them in entomological literature, in other words, 

 of names. 



The system of measurements used in this paper is int(nidcd to 

 enable the student, if he so desires, to draw an approximately 

 accurate outline of each form. Total length of the specimen mea- 

 sured is given in units and hundredths of millimeters; all of the 

 other measurements are ratios or readings from an eyepiece mic- 

 rometer each division of which has, with the magnification used, 



•■'A jjapcr especially devoted to this suhjeet is in Entomological News, xxxi, 

 No. 2, Feb. 1920, pp. IT-.W, and No. 3, March, 1<)2(), i)p. (Il-Cj"). 



