8 NORTH AMERICAN BLATTIDAE 



The dorsal surface of the abdomen, including the median seg- 

 ment, is greatly specialized in males of many species, and offers 

 fixed characters of the greatest diagnostic importance. This is 

 not true of females, though in some species some differences, usu- 

 ally only of degree, occur. 



The supra-anal plate in males of certain species is important in 

 form and structure. The form of this plate has also been consid- 

 ered diagnostic for certain subfamilies, but we have been unable 

 to determine the value of such features. This plate is much more 

 simple in females and often shows variability in contour in many 

 species; in this sex it is rarely of diagnostic importance. 



The cerci are of different types in many groups and genera. 

 When specialization occurs, it is normally more decided in the 

 male sex. In some groups specific diagnostic features are found 

 in the male cerci, ^ such is very rare in others.* 



The genitalia concealed between the male supra-anal and sub- 

 genital plates are very often of decided specific diagnostic value. 

 Unfortunately these are difficult to study in dried material. ^ 

 Little of diagnostic value is to be found in the anal chamber of 

 females. 



The subgenital plate in males of some species is important in 

 form, its appendages frequently showing other characters of highly 

 diagnostic importance. This plate is represented by a number of 

 distinct types in females, ^"^ but rarely shows features of specific 

 diagnostic value. 



^ In the genus Pafichlora the male cereal characters are of great importance in many- 

 species. See Hebard, Ent. News, xxvii, p. 218, (1916). 



8 See under Parcoblatta uhleriana (Saussure), showing diagnostic specific male cereal 

 characters, alone of the species of Group Ischnopterites here considered. Somewhat 

 similar specialization, but of no diagnostic value, due to its variability, is sometimes found 

 in both sexes of Parcoblatta pensylvanica (De Geer). 



" In the Polyphaginae these features are found to be of the highest importance, but 

 removal of the subgenital [)Iate, before study of dried material, is almost always neces- 

 sary. 



'" It is particularl>- interesting to note that a valvular type of the female subgenital 

 plate, which has long been considered an important characteristic of the Blattinae, is 

 also found in the Corydiids, Ilolocompsa nitidula and Compsodes delicatulus and in the 

 Polyphagid, Ilomoeogamia mexicana, but of a different general type in these species. 



