206 - [Sei>tcniber, 



ON THE STRIDULATORY ORGANS OF TEOX. 

 BY DR. D. SHARP, F.E.S. 



Probably almost every one who has handled a living specimen 

 belonging to this extensive genus is aware of its power of producing 

 sound ; a sound which can be felt when the insect is handled, as well 

 as heard. Hitherto, the way in which the sound is produced has not 

 been made out. Lacordaire (Gleuera des Coleopteren, iii, p. 151) says, 

 "ail the species, when seized, contract the head and legs and produce 

 a sound caused by the rubbing of the abflomen against the elytra." 

 Harold says, in his Monograph of the genus (Col. Hefte, ix, p. 13), 

 " the upwards directed portions of the sides of the ventral rings, 

 which are covered by the elytra, are very finely gj'anulated, and by 

 rubbing against the inner surface of the elytra produce the well-known 

 chirping which the creatures emit when handled." Leconte and Horn 

 say (Classif. N. Amer. Col., p. 247), '' the genus Trox possesses a 

 distinct stridulating organ ; it is an elliptical plate with pearly re- 

 flections occupying the upper part of the extreme face of the ascending 

 portion of the first ventral segment, and is covered by the elytra ; on 

 the inner surface of the elytra, near the margin, about opposite the 

 metathorax, is an oval, smooth, polished space, which has probably 

 some connection with the stiMdulating organ." On examining these 

 structures I was struck with the fact that they are totally dilferent in 

 their sculpture from all the other stridulating organs that have been 

 detected in beetles ; and at the same time they appeared to me very 

 ill-adapted to perform the function ascribed to them. I according!}^ 

 made a careful examination of two different species of Trox, and was 

 soon rewarded by finding the usual form of Coleopterous stridulating 

 organ, though the parts are different in their positions from those of 

 any other beetles, so far as we know at present. 



The elytra of Trox are so closely fitted together that they can 

 withstand great pressure. If taken off and examined it is found that 

 there is on the apical half of each, quite close to the suture, a fine 

 raised carina, the surface of which is beautifully striated. On 

 scratching this surface with a knife-edge, sound such as is characteristic 

 of Trox is heard. In order to scratch these strise there exist on the 

 penultimate dorsal segment two fine, sharply raised, ridges. One of 

 them is placed on the anterior margin of the segment, and in a large 

 North American species (which I am unable to name, sent me from 

 Arizona by Mr. Wickham) attains great perfection ; the second ridge 

 is placed just in front of the posterior margin of the segment. In 



