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- 

 lidce), 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 from Senegal, the 

 right mandibZe 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, compoimd 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 Crochard edition of the Animal 

 Kingdom (Ins. pi. 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. 



