1918.] F. H. Geavbly : Passalidae of the World. 5 



Flightless species consequently tend to bear a strong resemblance to one another, 

 especially as regards the general shape of the body, and Bates (1886, pp. 2-3) divided the 

 America» Passalidae into two sections on this character alone (see below, p. 6). 



The extent of the modifications differs greatly in different species, and the relation 

 which they bear one to another is not always the same. Thus in American species the union 

 of the elytra tends to precede the modification of the metasterrmm, while in Indo- Australian 

 species the reverse is the case. Similarly, reduction of the dentition, which seems to be to 

 some extent associated in American groups with loss of the habit of flight (see below, p. 9) 

 is only found in Indo- Australian forms (where it reaches its maximum development) among 

 species which show no indication of this. 



In the Indian Pleurarius brachyphyllus, in which the wings are fully developed, the 

 union of the elytra is not indicated in the pupa and is imperfect or absent in the newly 

 hatched adult. This appears to be the case in some other species also, and it seems likely 

 that the elytra may remain separate throughout life in certain individuals. I have not seen 

 pupae of any of the more highly modified species. 



Genitalia and Sexual Distinctions. 



Very little appears to be known of the genitalia of the Passalidae. Sharp and Muir 

 /1912, pp. 579-580, pi. xliv, figs. 1 1-13«) found two forms of male genitalia to exist, one in 

 which " the basal piece and the lateral lobes form one piece, either by consolidation or the 

 suppression of the basal piece " and one in which " the tegmen consists of two distinct 

 pieces, the basal piece and the lateral lobes." The former they found in the genus 

 Aulacocyclus, the latter in all the other genera they examined ; but their observations were 

 very restricted. I have been able to add to these observations to some extent ; but the 

 results were not such as to warrant any extensive investigation, since all the genitalia 

 examined proved to be very much alike, except in the Aulacocyclinae. Here both the types 

 described by Sharp and Muir occur, one in one group of the subfamily and the other in the 

 other, showing that the difference they found in Aulacocyclus is not a distinctive character 

 of the Aulacocyclinae as a whole, as suggested in my previous paper (p. 191). The only 

 other positive result of my investigations" was a curious fact which emerged in connection 

 with species in which the central tubercle varies greatly in size. In these it was found that 

 the specimens in which it was largest and best developed were females, and not males as 

 would be expected by analogy with other groups. 



Classification, etc., including notes on the structure of the mandibles. 



Although the Van de Poll collection is a remarkably fine one, it is by no means complete. 

 There can, I think, be little doubt that a considerable number of described genera and species 

 have no separate existence ; but the absence from the collection of such distinctive forms as 

 Platyverres intermedins, and of other well-known species, affords sufficient proof that the 

 names of the missing forms are not all to be lightly relegated to synonymy. The number 

 of new species in so incomplete a collection, on the other hand, seems clearly to indicate 

 that the Passalidae of the world as a whole are less fully known than are those of the 

 Oriental Region dealt with in my previous paper. 



