Doctrine of Affinity and Analogy. 105 
stance in which it agrees with Pelidnota MacLeay, another 
South American type,) only the tip is uncovered. The latter, 
Mimela, has an elevated prosternum, and a metasternum with 
a very short anterior mucro, so as to leave the mesosternum 
visible ; whereas in the former, Areoda, the prosternum is not 
visible without dissection, and the anterior mucro of the meta- 
sternum is elongated so as entirely to cover and conceal the me- 
sosternum. ‘The abdomen also in Areoda is covered underneath 
with an infinity of very minute punctula, which give it a silky 
appearance; whereas in Mimela, and likewise Pelidnota, it is 
lævigated. 
Though Mimela agrees in most of its essential characters with 
Euchlora, it differs sufficiently to form at least a subgenus in a 
modern system. In the former the mandibulæ have only two 
teeth at their apex; in the latter they have three. In this also 
the body is covered with innumerable impressed puncta of the 
same size ; whereas in that the puncta are of two sizes, the larger 
scattered, the smaller almost invisible and quite covering the 
surface. In Euchlora the last dorsal segment of the abdomen 
and part of the last but one are uncovered, the very reverse of 
which, as we have seen, takes place in Mimela. Whether the 
inner claw of the four anterior legs is bifid at the apex in the lat- 
ter as it is in the former I cannot say, these tarsi being mutilated 
in my specimens. 
I shall here mention one very remarkable circumstance, no- 
ticed by no writer that I have met with, which distinguishes the 
mandibulæ of the tribes of Melolontha F., though less con- 
spicuous in Melolontha itself than in the Euchlora, Rutelide, 
Anoplognathide, Chalepus, &c. The molary part, or that which 
appears destined to comminute the food, is an orbicular or 
subquadrate flat plate at the inner base of the mandibles, 
scored out into numerous alternate transverse ridges and fur- 
VOL. XIV. P rows. 
