Soitnd-'produdion in the LamcUicorn Beetles. 719 



was formerly functional, or whether, although degenerate, 

 they are still capable of producing sounds of some kind at 

 the will of the insect. 



Double files of almost identical form occur in Heterony- 

 chus, Fodalgus, Grator, Callistcmonus, Pentodontosclicma, 

 Pimclopus and Xe^iodoriis. The last is of special interest 

 from the fact, very rare in Coleoptera, and not before 

 noticed in the present instancr^, that one sex only has the 

 vocal faculty. The genus is a rather isolated one, con- 

 sisting of a single West African species not closely related 

 to any other known foim. In the males the short ridges 

 composing the files are very numerous, sharp and strongly 

 elevated, but the propygidium of the female shows only a 

 few coarse scattered elevations, of which two loose clusters 

 vaguely represent the well-developed apparatus of the 

 other sex. The explanation of this striking inequality of 

 the sexes is not difficult. In the male the last dorsal 

 segment is turned inwards so as to become almost com- 

 pletely ventral, as in the males of many other Lamelli- 

 corns. In the female this part of the body occupies the 

 normal position, and the consequence is that the preceding 

 segment occupies a more anterior situation than in the 

 male. As there is no corresponding difference in the 

 elytra, the extremities of these, which scrape the files of 

 the male, do not coincide with the propygidium of the 

 female. It seems probable that a simultaneous change of 

 form has taken place in both sexes and that this has 

 resulted in the stridulating apparatus in the female becom- 

 ing useless and therefore degenerate. 



There is a genus of Brazilian Dynastida3 (Acerus) which 

 Lacordaii'e, in his "Genera des Coleopteres " (vol. iii, p. 

 415), has expressly stated to be without stridvilating 

 organs. This, however, I have found to be a second case 

 like that just mentioned, and Lacordaire's statement is no 

 doubt based upon the examination of a female, in which 

 sex the propygidium is simply covered with not very fine 

 granules. The insects are rare, but from the examination 

 of a single male specimen in the British Museum I have 

 found that in this sex there is a well-deveh»ped file cover- 

 ing the entire median part of the segment, as in Orijdcs, 

 etc. It is a remarkable fact that, with the exception of a 

 single species (the Hispid, Sirilisiia iiiijjerialis, in which 

 the organ is a highly peculiar one), the only beetles 

 hitherto known to have stridulating orijans in the male 



