70 



respect within the limits of a genus to justify the importance 

 that Lacordaire assigns to it. For example, Cheiroplatys is 

 placed in the Group having that joint feebly triangular and 

 Horonotus in the other Group, but there is really very little 

 difference between the degree of triangularity in some species 

 of Cheiroplatys and some of Horonotus. This same character 

 moreover is variable with sex, the males (in at least some 

 species) of Pimelopus, for instance, having the basal joint of 

 the hind tarsi quite evidently less strongly dilated at the apex 

 than their females. The result of all this is that a female 

 Dynastid cannot be confidently referred to its Group by the 

 use of Lacordaire's subtribal or group characters, and the 

 same remark may be applied to Burmeister's classification, at 

 any rate in respect of Australian species, that author also 

 basing his main aggregates on sexual characters. 



The classification of the Dynastides, excluding characters 

 that either are sexual or cannot be ascertained without dis- 

 section, is no doubt extremely difficult, and some characters 

 that one would naturally turn to as hopeful are found to 

 fail when a long series of species are examined. The form af 

 the mandibles is one of those, the presence of teeth or notches 

 on the external outline being very conspicuous in some 

 mandibles and entirely wanting in others ; but it is cer- 

 tainly not strictly and invariably a generic character, the 

 greatest possible diversity existing within the limits of Isodon 

 (for example) in the form of the external outline of those 

 organs ; in the species which I take to be I. pecuarius, Reiche 

 (for instance), the external edge of the mandibles, is strongly 

 dentate, while in the species that I have no doubt is 

 /. australasice, Hope, the external edge is not even distinctly 

 sinuate, although there is an obtuse projection directed for- 

 ward at the apex — not on the lateral margin — which is, no 

 doubt, what Lacordaire refers to when he says "mandibules 

 terminees en dehors par une dent seule large et obtuse." 

 So again with the greater or less projection of the mandibles ; 

 it varies either specificially or according to their attitude 

 when the insect died. In Novapus a generic character is 

 asserted "mandibular crassce porrectce," which is the case with 

 all my specimens of N. crassus, Shp. (the typical species), but 

 in the closely allied N . adelaidce, Mihi, the appearance of 

 the mandibles is scarcely different from that in Isodon ems- 

 tralasice, Hope. 



The presence and form of organs of stridulation again 

 is not always generic. In Isodon puncticollis, Macl., they are 

 present as two short lines of a transverse rugae, in I. aus- 

 tralasice they are wanting, in an undescribed species before 

 me which I hesitate to separate from Isodon they are present 



