14 LUCANID^ AND PASSALID^. 



Unfortunately a very considerable number of tlie genera 

 hitherto arcejjtcd in this grou]) are distinguislied solely by 

 peculiarities of tlie male antl, in the case of females of which 

 the other sex is not certainly known, not only must the species 

 remain unknown but even a generic name cannot be supplied. 

 Worse still, since the features distinctive of the male are 

 inconstant and, with diminishing size, tend to fade away, such 

 generic characters are often absent, not only in all the specimens 

 of one sex, but in many of the other. It is obvious that, 

 instead of facihtating it, such a system is a very serious 

 obstacle to nomenclature. I therefore propose to recognize 

 only genera in which distinctive features are to be found both 

 in male and female. In groups of animals in which one of 

 the sexes is rarely found or is rudimentary in character, it 

 may be impossible to apply this rule, but in the Lucanid^ 

 the two sexes are fully developed and approximately equal 

 in numbers. The characters of the females are relatively 

 constant and much more easily defined than those of the males, 

 and experience shows that the features of most importance in 

 classification are to be found in both sexes. When the male 

 alone of a species has been known, a particular feature may have 

 been quite reasonably supposed to be of generic importance ; 

 but subsequent discovery that it is found in one sex only 

 should be accepted as proving that assumption wrong. 



In these beetles the feature that first strikes the eye is of 

 course the enormous development of the mandibles, or 

 " horns," of the males, which, in most species, differ in toto 

 from those of the females. The mandibles of the latter are 

 rather constant both in size and shape, obviously serving the 

 same practical purposes throughout tlie group. They are 

 short and sharp, the tips crossing one another, the outer edge 

 simply rounded and the inner edge usually bearing a stout 

 tooth for givhig increased gripping power. The mandibles 

 of the male, on the other hand, except in the few genera where 

 the two sexes are alike and in a small number of exceptional 

 species of other genera, such as Dorcus derelictus and Lncamts 

 gracilis, in which the organs are little larger in the one sex 

 than the other, convey no such suggestion of practical efficiencj^ 

 in well-grown specimens at least. In many cases they reach 

 a size (in Lucanus cantori and L. laminifer, Plate III, figs. 1 

 and 5, for example) which must inevitably restrict the freedom 

 of movement of the bearers and exhibit fantastic shapes 

 which, if we consider them as weajions or tools, suggest only 

 a high degree of inefficiency. The great difierence between 

 the sexes in the mandibles entails other differences. The 

 enlargement of the mandibles may be accompanied by a 

 great enlargement of the head and often, as in the genus 

 hnmnns, the head bears strong ridges or outgrowths wliich 



