Soimd-'produciion in the LaiiicUicorn Bcdkti. 727 



Wc now covno to tlio Gcotrupida*, of which tlio familiar 

 typo, (joolriq^es, was ono of the oatliost insects to have its 

 musical power recorded. Tlic instrument in this genus is 

 very similar to that oi Idiosioma jnst dcscriboLl, the file 

 being found upon the hind coxa and having the form of a 

 narrow obli(|uc bar made up of microscopic ridges. But 

 the situation is not the sumo, for whereas in Idiostuma, as 

 in the true Orphniduo, it occupies the outer end of the 

 coxa, in Gent'nqxifi it is at the inner end. It seems in all 

 the species to bo scraped by the lander margin of the 

 socket, which forms a sharp edge. Landois, in iiis 

 " Thierstimmon," speaks of a " Geotrupes sflcndidnhfi" which 

 is without the instrument, but T have been unable to 

 discover what he referred to. 1 believe it to exist in all 

 species of every section of the genus, defined in its widest 

 sense, and to differ only in th^ degree of fineness of its 

 component ridges, and consequently in the pitch of the 

 note produced. For instance, the instrument is moder- 

 ately fine in Geotrupes siercorarius and mutator, coarser 

 in G. si/lvalicus, alpiiiits and Jdostius, and very fiiu; in 

 G. Typhmus and o'eticsus. 



Fuuling the organ so constant through the very various 

 species of Geotriqjes, I anticipated that it would be found 

 more or less general in the family Geotrupida3, but was sur- 

 prised to find it elsewhere only in a group of Australian 

 species of the genus Bolbocaras : e. g. IJ. Heichei, rhinoeeros 

 and frontal e. I subsequently f(-)und that so long ago as 1805 

 the collector Odewahn had reported that an Australian 

 species of Bolboceras produced " a noise like a Longicorn, 

 by moving the small pulvilli beneath the hind coxaj." 

 Tliis was recorded by Pascoc,* who did not identify the 

 species referred to, and who afterwards •!" tried to amend 

 tliis very curious explanation by the scarcely more exact 

 statement that "striae are visible on the dorsal surface of 

 the coxa^., and similar but smaller stri;u within the cavity." 

 The organ is really a modification of that characteristic of 

 Gcotru'pcs, perhaps a more primitive condition. Instead of 

 the single obli(|ue roll of closely-packed ridges upon the 

 hind coxa of the latter we find the ridges arranged in a 

 series of wavy bands from foiu" to eight or nine in number. 

 In Bolboceras Reirhei (PI. XXXVI, fig. S) there are four 

 bands approximately equal and parallel, composed of 



* Proc. Ent. Soc, 18(55, p. HI. 

 t Op. cit., p. 107. 



