482 EXTERNAL ANATOMY OF INSECTS.® 
discover a minute membranous protuberance under each 
angle of the nose. Something similar may be observed 
in some species of Aszlus. In the Orthoptera, especially 
in Blatta, Phasma, and some Locusta, two roundish 
or square pieces, close to each other on the lower part 
of the nose, represent the nostrils?; but in many, as 
Acrida, the whole lower part differs in substance from 
the upper, and represents the Rhinarium.— With re- 
gard to substance, in the chafer-tribes, at least those that 
feed on leaves or living vegetable matter, as the Melo- 
lonthide, Anoplognathide, and in many other insects, 
the rhinarium is of the same substance with the rest of 
the head; but in Acrocinus, Staphylinus, Necrophorus, 
&c., it consists of membrane. 
ii. Postnasus*.—This is a part that appears to have 
been confounded by Entomologists with the front of in- 
sects; in general, indeed, it may be regarded as included 
in the nose, and does not require separate notice: but 
there are many cases in which it is distinctly marked out 
and set by itself, and in which it forms a useful diagno- 
stic of genera or subgenera. ‘There is a very splendid 
and beautiful Chinese beetle, to be seen in most collec- 
tions of foreign insects (Sagra purpurea), in which this 
part forms a striking feature, and helps to distinguish 
the genus from its near neighbour Donacia. If you ex- 
amine its face, you will discover a triangular piece, below 
the antennee and above the nasus, separated from the 
latter and from the front by a deeply impressed line: this 
is the postnasus or after-nose. Again: if you examine 
any specimens of a Hymenopterous genus called by 
® Prate VI. Fic. 4. ¢’. > Prares VI. VII. b. 
