OX MELOLONTHINE BEETLES OF THE GESTUS ECTINOITOPLIA. 267 



16. A Revision of the Melolonthine Beetles of. the Genus 

 Ect'uiohoplia. By G. J. Arrow, F.Z.S., F.E.S. 



(Plate I.) 



[Received January 6, 1921 : Read April 5, 1921.] 



The genus Hoplia contains an enormous number of species, 

 often of great beauty but extremely variable and difficult to 

 discriminate. Attempts to divide it into smaller genera have 

 not been very satisfactory, but Ectinohoplia, containing a number 

 of Oriental species of moderately large size, distinguished by the 

 propygidium not being covered by the elytra, in addition to the 

 existence (generally) of a tuft of bristles at the extremity of the 

 elytral suture, is fairly well defined. Some of its species, 

 however, ha,ve not been referred to it, and others have been 

 described under more than one name. I have therefore 

 attempted a revision of the genus, and the accompanying key to 

 the species includes all those at present known to me as members 

 of it. The striking difference in the coloration of the scales 

 which distinguishes the two sexes of some of the species has 

 hitherto not been noticed. Contrary to the general tendency in 

 insects, the females of some of the species are remarkable for the 

 occurrence of splendid golden, silvery, or iridescent scales, 

 replaced by dull scales in the other sex. 



Although differences of this kind are not very unusual, it is 

 almost invariably the male which shows the brighter coloration ; 

 and it is therefore interesting to observe in the exceptional 

 instances here brought to notice that the brilliant clothing of 

 the females is almost confined to parts of the body where it is 

 concealed in the ordinary position. 



In the male of E. suturalis (Plate I. fig. 1) the whole of the 

 scales, of the upper and lower surface alike, are of a uniform pale 

 non-brilliant blue, in striking contrast to the yellow and golden 

 scales of the female (Plate I. fig. 3), in which, however, those of 

 the upper surface are not brilliant, while upon the abdomen they 

 are of the richest gold and pale metallic blue. Under a high 

 power of the microscope the difference is seen to be due to a, 

 fundamental difference in the individual scales. The golden scales 

 of the female are deeply pigmented and completely smooth, but 

 the dull blue scales. of the male are devoid of pigment and the 

 surface is covered with a dense clothing of fine hairs or hairlike 

 outgrowths, to which the opacity and blue colour are evidently 

 due. A remarkable change is effected by moisture upon 

 the opaque scales, which immediately become metallic and 

 glistening. 



E. auriventris Moser has a similar sexual difference, the 

 scales of the lower surface, pygidium, and propygidium being 

 golden in the female and opaque orange-coloured in the male. 



Proc. Zool. Soc.— 1921, No. XIX. 19 



