720 Mr. Gilboii, J. Arrow on 



side of" one of the dorsal sogmonts a curious club-shaped 

 appendage, very small and evidently extremely hard. The 

 lateral ])arts of the back arc formed, as in other Larnclli- 

 corns, by the bent-round ventral segments and are com- 

 paratively rigid, while the intervening part is delicate and 

 flexible. At the inner limit of this rigid part of the third 

 segment from the apex is the small chitiuous prolongation 

 referred to, pointing obliquely inwards and backwards, i.e. 

 towards tiie apices of the elytra (PI. XXXVI, lig. %i). In 

 most of the s})ecies of Oi'Iiodivitu in which I have examined 

 it, this organ has a distinct neck and bulbous part, and 

 under a, high power of the microscope the latter is seen to 

 be studded with projections placed in rings around it. By 

 the extension and contraction of the abdomen these would 

 produce friction with the fdes upoa the elytral folds, and, 

 if it appears rcniarkablo that the sound generated by such 

 minute structures shoukl be audible to human ears, it 

 must be remembered that the total area from which the 

 sound is produced is considerable in proportion to the size 

 of the insect, and the really striking thing is that the voice 

 of so small a cieaturc should be audible to us at all. 



The I'orm of the dorsal stridulators differs according to 

 the species, but the description just given will aj)ply to 

 the two European species and to the American species 

 which I have examined. There are some Oriental forms, 

 however, which are conspicuous both for their size and 

 bright markings, and here a rather different form occurs. 

 In Odwdieus maculipejinU, for example, the organ is not 

 club-shaped, being widened instead of narrowed at its 

 base, and the projections take the form of short, sharp 

 obli(iuc ridges at its extremity (PI. XXXVI, figs, 3, 3rt, 8Z>). 



Another of the peculiarities of this genus may be 

 related to the vocal apparatus. Each of the four posterior 

 legs bears a pair of long spines at the extremity of the 

 tibia, and upon the middle tibia the inner one of these 

 spines is })articularly long and stout and upon one side is 

 deciply notched so as to form a comb, quite unlike any- 

 thing known in any other beetles. An important function 

 of the legs of most insects is that of cleaning the body, and 

 from its position it seems not improbable that this 

 remarkable comb may serve to remove any adhering 

 particles from the stridulating organs, to which naturally 

 absolute cleanliness is essential and the nature of whose 

 surface must make them rather difllicult to clean. 



