b NORTH AMERICAN BLATTIDAE 



Maxillary palpi, though differing decidedly in different genera, 

 of little specific diagnostic value. Individual slight variations are 

 found in the length of the three distal joints. 



Pronotum in size, form and contour showing frequent generic, 

 occasional specific, diagnostic features. Some variation, how- 

 ever, in such useful features as point of greatest width and depth 

 of discal sulci, when present, almost always occurs. The form 

 varies with reduction in the organs of flight, this most noticeable in 

 a greater truncation of the caudal margins, which makes the latero- 

 caudal angles much more acute, moves the point of greatest width 

 caudad, and develops a more even generalfconvexity of the pro- 

 notal surface. Where great differences occur in the organs of 

 flight of the sexes of the same species, the differences in the pro- 

 notum are likewise decided. 



The tegmina and wings offer features of decided generic impor- 

 tance. These must always be considered with allowances for the 

 forms in which reduction occurs in one or both of the sexes. ^ The 

 general plan of the veins, particularly the direction of the tegminal 

 discoidal sectors, is the most valuable and least variable generic 

 feature, but in some groups the division of certain veins is of decided 

 generic diagnostic value. « Differences in the number of rami of 

 certain veins are, in all the forms we have considered, attributable 

 to mere individual variation. In some groups the folding of the 

 wing, intercalated triangle or appendicular field, is of importance, 

 both generic and specific, the lesser differences, of specific value, 

 being subject to slight variations. When reduction in length 

 occurs, particularly when this has reached a decided degree, the 

 general character of such is often of decided specific value in one 

 or both sexes, though occasionally in many species some variation is 

 encountered. The costal veins of the wings sometimes show im- 

 portant features, as do the rami of the discoidal vein. 



5 Much of the worst confusion in the past, both generic and specific, has been due to 

 failure to recognize this factor. Minor differences in venation have also, at times, been 

 incorrectly supposed to warrant specific separation. On the other hand, ignorance of 

 the specific rather than generic value of tegminal and wing reduction, in one or both 

 sexes, led to error in generic designation. 



8 Thus the discoidal vein of the tegmina and wings forks in Symphce and Xestoblatta 

 alone of the known American genera of the Group Ischnopterites. 



