2 78 RUTELINJE. 



of closely similar species, some of which occur in enormous 

 profusion and have been found to cause serious damage to 

 cultivated crops, upon the roots of which the larvae feed. 



In the genus Adoretus, which contains the vast majority of 

 the known species, the remarkable formation renders it necessary 

 for one side only of the mouth to be used at a time. A leaf (of 

 Cassia) attacked by Adoretus versutus which has been sent to me 

 has oblong holes eaten out of it in pairs, the beetle having 

 apparently fed first on one side and then on the other, moving 

 slowly backwards but not otherwise altering its position, and 

 leaving a narrow strip of leaf intact in the middle. If this is 

 characteristic of the species of this genus it will make the recog- 

 nition of damage due to them simple and certain, but it still 

 awaits confirmation. 



At my request, Mr. F. H. Gravely has carefully watched the 

 feeding process in Adoretus versutus, and the result is described 

 by him in "Records of the Indian Museum," xi, 1915 (p. 499). 

 He finds that the insect rests upon the flat surface (generally the 

 lower surface), not the edge of the leaf, and bites holes in the 

 latter, turning its head slightly to one side or the other to do so 

 and using only the organs of that side of the mouth. The 

 principal instrument in this operation is the peculiar broad fan- 

 shaped maxilla, which scoops out and draws into the mouth 

 small quantities of the soft leaf-tissue. Mr. Gravely thinks that 

 an important function of the mandibles, apart from the basal 

 masticatory mill, is to protect the maxillae and to close the two 

 mouth openings when not in operation. 



Key to tJte Genera. 



1 (8) Labrum without a median pro- 



cess. 



2 (3) Clypeus straight or regularly 



rounded .................. PRODORETUS, Breus., p. 279. 



3 (2) Clypeus pointed or lobed. 



4 (6) Clypeus acuminate .......... OXYADORETUS, g. n., p. 281. 



5 (4) Clypeus lobed. 



6 (7) Cl 



Clypeus narrow, consisting of 

 two lobes ................ SCHIZADORETUS, g. n., p. 283. 



7 (6) Clypeus broad, consisting of 



four lobes ................ PH^ADORETUS, Reitt., p 284. 



8 (1) Labrum with a median process. 



J) (10) Process of the labruni free, not [p. 28o. 



bisecting the mouth ........ PACHYRRHIXADORETUS, Oh., 



10 (9) Process of the labruni bisecting 



the mouth, not free. 



11 (12) Mandibles reduced, process of [p. 288. 



the labruni minute ........ HETEROPHTHALMUS, Bl., 



12 (11) Mandibles large. 



13 (18) Process of the labrum pointed. 



14 (17) Process of the labruni small, 



not dilated nor concave in 



front. [p. 289. 



15 (16) Labrum serrate at the sides . . TRIOONOSTOMUSI, Burm., 



