; 
1 
q 
] 
199 
Hymenoptera and Coleoptera, than had hitherto been bestowed 
thereon. In the higher orders of animals so much importance had 
been given to this character, that it was remarkable that, in general, 
entomologists contented themselves with examining, describing, and 
figuring a single mandible as affording a sufficient diagnosis of the 
structure of both of the mandibles, overlooking the necessary result 
which arose from the circumstance of the horizontal instead of per- 
pendicular action of these organs in insects, and the variation in the 
position of the teeth which such action must necessarily induce. In 
general, indeed, the teeth of the mandibles were not greatly developed, 
and there was a general similarity between the two jaws; but when 
these organs are of an increased size, and especially when the extre- 
mity of one jaw laps over that of the opposite one, a diversity in the 
dentition will necessarily exist. It was likewise necessary to examine 
the mandibles of both sexes of a species, as it occasionally happened 
that there was considerable difference in their dentition. These ob- 
servations were illustrated by the case of the Tiger Beetles (Cicinde- 
lide), which offered a much greater range of diversity in their denti- 
tion than had hitherto been supposed. It was chiefly to the genus 
Megacephala that Mr. Westwood directed the attention of the 
members. 
In the type of that genus (Megacephala senegalensis, Latr., Dej., 
Cic. megalocephala, Fabr.), an apterous species frum Senegal, the 
right mandible of the male has two large, nearly equal-sized, acute 
teeth in the middle of the inner margin, the extremity being hooked 
and very acute; there is also a small tooth at the base of the large, 
broad, compound basal tooth. The left mandible is nearly similar, ex- 
cept that the two teeth in the middle of the inner margin are unequal 
in size, the upper one being the smaller of the two. The figure of the 
jaws of this species, given in the Crechard edition of the Animal 
Kingdom (Ins. pl. 16. f. 2 a), is very incorrect, being apparently 
reversed. The dentition of the female is almost identical with that 
of the male. In the allied bat-winged African species, Megacephala 
4-signata, Dej., from Senegal, the toothing of the mandibles is simi- 
larly arranged, but the two teeth in the middle of the inner margin, 
in both sexes, are broad and obliquely truncate. In the male of 
M. euphratica (which has recently been observed to extend from 
Spain to India), the teeth are nearly as in M. senegalensis, except 
that the subapical tooth of the left mandible is considerably smaller. 
But in the species lately received from the north-west of Australasia 
(M. Australasia, Hope), we find a different arrangement as well as 
number-in the teeth, the right mandible having three teeth in the 
middle of the inner margin (exclusive of the small tooth* at the base 
of the upper side of the large compound basal tooth), the upper one 
small, the middle one very small, and lower one large, all being acute.. 
The left mandible has also three teeth in the same position,—the 
* This small tooth exists in all the species, and in both sexes; and as it appears 
‘. to form part of the great basal tooth, I have omitted noticing it in the descriptions 
given in this paper. 
