96 BRITISH CICADA. 



face, with its frons (almost always striated, indented, 

 or barred transversely with brown), is a marked charac- 

 teristic, which tends, we may say, to a clear identifi- 

 cation of the whole group. 



The genitalia, likewise, are apparently framed on 

 the lines of a common type, whether we consider the 

 most highly specialised examples of Cicada or those of 

 the more simple Typhlocybidse. 



The deeply chambered caudal process, with its 

 variously shaped style, may be well studied in Issus, 

 Cixius, Liburnia, Idioceriis, and Deltocephalus, up to the 

 end of Typhlocyha. The variously shaped male genital 

 styles may be followed through Delphax to Gnathodus, 

 and the curiously recurved, flagelliform, intromittent 

 male organ, may be seen exampled in the figured 

 details of Plates XII., XIV., XVIII., and others. 



The serrated ovipositor, with the complicated laminae 

 which form its sheath, obtains throughout the whole 

 group from Cicada to Ztjgina. Although this is the last 

 genus of the series, and the species are less differenti- 

 ated, the insects contained within it are by no means 

 lacking in interest either as to form, colour, or 

 ornamentation. 



The tasks of revising species and the collation of 

 synonyms are tedious, and attended also with responsi- 

 bility. Outward appearances may be misleading, and 

 the repeated appeal to the microscope for details, 

 though necessary, is often laborious. 



John Scott has noted the interesting fact that some 

 species, and more particularly those of the Delphacidse, 

 show such similarity that they may be broken up into 

 what he calls " parallel pairs," and that this similarity 

 is kept up both in the Macropterous and Brachelytrous 

 forms (see Ent. Mo. Mag. vii. p. 75). The resemblance 

 between several forms is indeed so close that, except for 

 certain divergences in the details of the pygofer, one 

 well-defined species can with difficulty be separated from 

 its mimic. How far such mimicry may prove to be pro- 

 tective will be the result of subsequent investigation.. 



