Oenera and Species of Blattidie. 163 



rotated outwards through some degrees, and, owing to a 

 greater or less elevation of its upper border, is now separated 

 dorsally from the disk of the proiiotum by a channel or groove 

 of varying depth. Frequently, though by no means always, 

 the development of the lateral bands is accompanied by a 

 sliglit upward reflection of the anterior margin of the pro- 

 notum. Tiic uj)per edge of this reflected border is continuous 

 with the U{)per edge of the lateral bands; the lower edge, 

 when seen from the ventral aspect, is occasionally continuous 

 with the lower edge of the lateral bands, as in Cyrtotria jalke^ 

 Gig.-Tos (PL X. fig. 19), in which case the lateral bands 

 are connected anteriorly with each other, but more frequently 

 the lower edge of the anterior reflection is not evident and 

 the lateral bands are not connected with each other anteriorly 

 (Pi. X. fig. 13). 



In the species of the genus Bantua (PL IX. fig. 10, D), 

 the rotation of the lateral bands has been carried still further, 

 /. e. outwards, downwards, and then inwards, so that now 

 the lateral bands form a very acute angle with the disk of 

 the pronotum and lie underneath it ; the gutter or channel is 

 obliterated, just as a fold in a piece of cloth vanishes when 

 the part of the cloth involving the fold is tightly wrapped 

 round some solid object. The outer border of the pronotal 

 disk is now the outer margin of the pronotum. A new species 

 of Pilema and a new species of Bantua described below 

 illustrate in a most striking and interesting manner the rota- 

 tion of the lateral bands of the pronotum, with concomitant 

 obliteration of the gutter separating the bands from the disk. 

 Finally, in the genus Derocali/mma (PL IX. fig. 10, E) the 

 lateral bands are bent still further under the disk and lie 

 in almost a parallel plane with it ; at the same time the pro- 

 notum is broader, it has reverted to the primitive flattened 

 shape, but its outer lateral margins are now not the morpho- 

 logical equivalents of the outer lateral margins of the primi- 

 tive type, but the equivalents of tlie inner boundaries of the 

 lateral wings of that. 



The whole series of specimens illustrates admirably the 

 evolution of a complex type of j)ronotum from a simple type, 

 the former superficially resembling the latter. It is by no 

 means often tiiat the entomologist is supplied with such a 

 series of gradations, and it is generally far easier to hazard a 

 suggestion as to the value to the species of certain structures, 

 than to elucidate their mode of origin. Here it is otherwise; 

 wo can see pretty clearly the steps whereby the pronotum of 

 Derocalymma evolved from a more primitive type, but the 

 value to the sppcifs of th^'-e variations in structure is by no 



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