15G Mr. R. I. Pocock on the 



but weaker crest is also developed upon the distal portion of 

 the corresponding surface of tlie femur of the second leg. 



The points of the denticulations on the elytra and abdo- 

 minal sterna are directed obliquely outwards and backwards, 

 so as to cause the greatest friction and produce the loudest 

 sound when the ridges of the femora are scraped against them 

 with the forward stroke of these segments *. 



No mechanism exactly resembling this in structure and 

 situation has yet been figured and described in the Coleoptera. 

 The nearest approach to it is to be found in the Cicindelid genus 

 Oxycheila and the Heteromerous genus Cacicus], both of which 

 stridulate by scraping the femora of the legs of the posterior 

 pair along the lateral area of the elytra. In these instances, 

 however, the organ consists of a transversely striated crest on 

 the elytra and a similarly striated strip of the integument of 

 the postaxial side of the femora. Again, the striated crests 

 on the elytra are lateral in position in Oxycheila and 

 Cacicus^ not inferior, as in Oraph!pterus. The position of 

 the crests in the latter is correlated with the expansion of 

 the elytra and of the abdominal segments without any 

 corresponding expansion of the mesosternal and metast^rnal 

 sclerites of the thorax, so that daring progression the femora 

 of the second and third legs work in a plane more nearly 

 approaching the horizontal than the subvertical plans in 

 which those of Oxijcheila and Oacicus move. 



That Graphfpterus variegatus is capable of stridulation is 

 no new discovery. To many travellers and residents in 

 Egypt it is probably a matter of everyday observation, and 

 60 long ago as 1832 an account of it was published by 

 j\I. Lefebvre J. According to this author, G. variegatus was 

 to be met with in the hottest part of the day. At night it 

 could not be found, in spite of diligent search. It lived on 

 the sand-hills, and was abundant in the localities it frequented. 



* "With the help of Mr. C. J. Gahaii and Mr. G. J. Arrow I have 

 ascertained that this organ is present in most of the JNorth-Afrieau 

 species rel'erred to Graphipterus and absent in those assigned to the same 

 genus from South Africa. The former also have a peculiar type of colo- 

 ration, not exhibited by the latter, which probably indicates a life amid 

 sandy surroundings. 



f C. J. Gahan, Tr. Ent. Soc. London, 1900, p. 448, pi. vii. tigs. 8, 8 n. 



J Ann. Soc. Ent. Fr. i. p. 311. I am indebted to Mr. 0. J. Gahan for 

 this reference. Lefebvre's account was apparently unknown both to 

 Darwin and to Landois, if we may judge from the absence of all refer- 

 ence to it in the former's 'Descent of Man' (1883) and the latter"s 

 ' Thierstimmen ' (1874). To this defect in the last-mentioned historical 

 account of sounding-organs is presumably to be traced the oblivion in 

 which Lefebvre's observations have seemingly rested since the time of 

 J^acordaire. 



