Genera 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 pronotum by a channel or groove 
of varying depth. Frequently, though by no means always, 
the development of the lateral bands is accompanied by a 
slight upward reflection of the anterior margin of the pro- 
notum, ‘The upper edge of this reflected border is continuous 
with the upper 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, asin Cyrtotria jalle, 
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 Xe ties 13). 
Inthe species of the genus Bantua (Pl. IX. fig. 10, D), 
the rotation of the lateral bands has been carried still further, 
7. 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 Derocalymma (PI. LX. tig. 10, EK) 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 the inner boundaries of the 
lateral wings of that. 
The whole series of specimens illustrates admirably the 
evolution of a complex type of pronotum from a simple type, 
the former superficially resembling the latter. It is by no 
means often that 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 ; 
we can see pretty clearly the steps whereby the pronotum of 
Derocalymma evolved trom a more primitive type, but the 
value to the species of these variations in structure is by no 
. ieee 
