Suund-'prodiuiion in the Lamellicao'n Beetles. 717 



male, instead of the reverse. I believe the difference 

 described to be directly connected with the more rapid 

 movements of the muscular and less corpulent male, the 

 musical result of the less rapid scraping of a more closely- 

 ridged plate being the same as that produced by more 

 vigorous movements upon one correspondingly coarser. 



In the numerous forms of Dynastidoe, inhabiting all 

 parts of the world, in which these structures are found, 

 there are considerable differences in the manner and 

 degree of development. In those in which the file is the 

 finest and most regular the segment bearing it is enlarged 

 at the expense of those adjoining. It may be produced 

 forwards under the elytra, or backwards, encroaching upon 

 the last segment (pygidium), which is immovably united 

 with it. In two of the genera, of which the sound, judging 

 from the great development and regularity of the ridges, 

 seems to be the loudest and most musical, viz. the 

 American Sccqitophilus and the Oriental Gamelonotus, the 

 extremely hard stridulatory plate is produced backwards 

 in a broad lobe, until in some species the pygidium is 

 almost crowded out of existence. The greatest degree of 

 sexual disparity in the organ which I have noticed in 

 Coleoptera is due to the much greater extension of this 

 plate in the males of the latter genus. When the pro- 

 pygidium has a file upon each side corresponding to the 

 two elytra a slight prolongation is frequently visible 

 beiiind each file. 



Although in Camelonotus the stridulatory plate is one 

 of the best-developed to be found among insects, and from 

 its extreme sharpness and regularity undoubtedly pro- 

 duces a high-pitched musical note, the corresponding 

 structures in many of the related genera are much less 

 fine and re^jular than is usual and must generate sounds 

 of a very different kind, probably in some cases a harsh, 

 grating sound. This may partly account for the fact that 

 scarcely any observations seem to have been made as to 

 the vocal powers of any of these insects, some of which 

 are of large size and very abundant. An unmusical 

 sound naturally attracts little notice, but it would be 

 remarkable that the notes produced by apparatus so 

 perfect as that of Scaptojohilus and Camelonotus and other 

 genera have not aroused attention, but that the extreme 

 paucity of biological observations recorded, notwithstand- 

 ing the multitude of collectors, is only too familiar. 



