98 FAUNA HAWAIIENSIS 



Group PLAGITHMYSIDES. 



The difficulty of distinguishing the three genera of Plagithmysides has considerably 

 increased in consequence of the discovery of additional forms. The characters 

 distinguishing Clytarlus from Plagithmysiis are, that in the former genus the hind 

 legs are clubbed and possess a long slender basal stalk. A sexual difference in the 

 form of the legs is constant in Clytarlus inasmuch as the femora of the female are less 

 clubbed than they are in the male (Plate VI. figg. 2 and 3). On the other hand 

 in the large majority of the species of Plagithniysus there is very little difference in 

 the legs of the two sexes, and the femora are never abruptly clubbed, and with a 

 long thin basal stalk. The females of Plagithniysus funebris, arachnipes and cristatus 

 possess however much more slender legs than their males, and therefore considerably 

 approach Clytarhis. The female of Clytarlus pennatus, has the legs but little clubbed, 

 and therefore there is but little difference between it and the females of the three 

 species of Plagithmysiis mentioned. 



The male of Plagithniysus adstatus approximates in the form of the legs to 

 Callithmysus. Thus this species is as it were the central point of the group, its male 

 approaching Callithmysus, while its female comes near to Clytarlus. 



It is also desirable to mention, in connection with the extraordinary reduction in 

 size of the abdomen in this group, that this character is subject in the females of the 

 same species to great variation. This is probably in connection with the growth of 

 the ovaries. Some of the females have the abdomen very small, while in others, 

 of the same sex and species, it is of the size normal in Coleoptera. 



Mr Perkins has observed that the extraordinarily complex stridulating organs of 

 these insects are brought into play during breeding, and that very frequent coupling 

 occurs, and this to an extent that is almost unknown otherwise in insects ; the 

 Plagithmysides are extremely active and are apparently both polyandrous and poly- 

 gamous. He has also suggested that the size of the abdomen influences the stridulating. 

 So that all the observations that have been made tend to show that the unequalled 

 complexity of the stridulating organs is correlative with the unusual system of copula- 

 tion and probably plays an important part in it. 



Clytarlus Sharp. 



Clytarlus Sharp, Ent. Mo. Mag. Oct. 1896, p. 238. 

 Clytarlus (pars) Sharp, Tr. Ent. Soc. London, 1879, p. 102. 



All the species of Clytarlus, except C. abnormis, are attached to one of the two 

 Acacias, Sophora chrysophylla and Acacia koa. They are rare and difficult to obtain. 

 The material before me is not adequate for the satisfactory elucidation of these very 

 difficult insects. 



