EXTERNAL ANATOMY OF INSECTS. 565 
nalis, &c. the structure at first sight seems different, for 
apparently the prosternum is received by the anterior 
fork of the mesostethium ; -but if you proceed to separate 
the manitrunk from the alitrunk, you will find that the 
true mesosternum of the usual form is quite covered by 
this point, which curves towards the breast, is longitu-: 
dinally concave to receive the point of the prosternum, 
and permit its motion in the groove. In some Hetero- 
merous beetles, as the Helopide, &c. this part is an- 
teriorly bilobed, so as to form a cavity which receives 
the point of the prosternum when the head is bent down: 
in Helops nitens this sinus represents a crescent; in 
Cistela Ceramboides it is shaped like the Greek letter y; 
in the Lady-bird (Coccinella) it assumes nearly the shape 
of a Saint Andrew’s cross; in Spheniscus? the mesoster- 
num is wide, concave and wrinkled, with an anterior 
and posterior sinus; while in the analogous genus Eroty- 
Jus» itis convex anteriorly, and posteriorly more or less 
rounded; in Doryphora it is a long, robust, subconical 
horn, often standing at an angle of about 45°, overhang- 
ing the prosternum. 
In the genus last named, though its mesosternum in its 
direction and appearance resembles that of many Peta- 
locerous beetles, yet it is separated by an evident suture 
from the mesostethium ; but in the last-mentioned tribe 
* Linn. Trans. xii. t. xxii. f. 4. 
> A remarkable instance of analogy is afforded by this genus. In 
Erotylus there are two groups ; one distinguished by gibbous elytra, 
and the other by flatter ones. The same distinction is observable in 
Spheniscus ; for to this genus belongs Helops fasciatus Oliv., which re- 
presents the flat Hrotyli, and even individually Hrotylus trifasciatus 
Oliv., E. fasciatus F. 
