Sououl-iwodudion in the Lamellicom Beetles. 725 



which I have found this organ is not veiy close either to 

 Orphnus and its alUes or to any other known beetles. 

 There are parts of three abdominal segments forming the 

 coxal cavity, and at the bottom of the cavity is excavated 

 a pit which extends the greater part of its length. The 

 outermost edge of this is sharply raised, and it appears to 

 be against it that the coxal file rubs, the pit providing the 

 open space in which the chords can freely vibrate. In the 

 other genera just mentioned the expansion of the coxa 

 beyond the lip of its socket brings the vibrating ridges in 

 each outward movement of the coxa outside it ; while in 

 Heliocojms the production of the microscopic ridges across 

 alternate slight elevations and depressions confines the 

 contact to a point, leaving the great part of each " string," 

 as in a violin, always free. 



Among the genera at present placed with the Orplmidge 

 there still remains a large and very peculiar series of small 

 beetles called Ochodmiis. These, which are less than a 

 quarter of an inch in their average length, inhabit many 

 parts of the world but are rarely found ; and their manner 

 of life, which from their structure is certainly peculiar, 

 seems to be unknown. The hind coxae are here diiferently 

 formed to those of the true Orphnidas and show no trace 

 of any vocal apparatus — indeed all parts of the frame- 

 work are less hard than in those and other stridulating 

 Lamellicorns, and I should have supposed them to be 

 voiceless had I not found it mentioned by Dr. G. H. 

 Horn (Trans. Amer. Ent. Soc, 1876, p. 180) that the 

 North American species utter a sound. This led me to a 

 more careful investigation and the discovery of a new and 

 remarkable apparatus. The propygidium of these beetles 

 is furnished in the middle with peculiar grooves and 

 spines, differing considerably in the different species but 

 all serving to hold the elytra firmly in position. The 

 latter, like the remainder of the general surface, are more 

 or less hairy outside, but their inner surface is polished 

 and shining except for a kind of roll or thickening extend- 

 ing from the tips along and within the outer margins 

 (PI. XXXVI, fig. 26'). Tliis is doubly striated, producing 

 an " engine-turned " surface ; or more probably this effect 

 is due to a diagonal series of modified spines placed in 

 close juxtaposition. The abdomen is little chitinized, and 

 seems too soft to bear any part in stridulation, but when 

 removed, examination with a strong lens reveals on each 



TRANS. ENT. SOC. LOND. 1904. — PART IV. (DEC.) 47 



