76 [April, 



ON THE BRITISH SPECIES OF RIOLUS, Mulsant. 

 BY JAMES EDWARDS, F.E.S. 



'J'he members of this 2;cnus are easily distinguished from our 

 other native Hehninthince by their eleven-jointed antennse and the 

 want of sublateral raised lines on the thorax. I am indebted to 

 Mr. Champion for the opportunity of introducing R. sodalis, Er. 



The characters which seem to me to serve best for the separation 

 of our species are set out in the following table ; but it should be 

 noted that considerable variation exists amongst these insects, and 

 that it is useless to expect index-characters to which there shall be 

 no exception. For instance, I have a specimen of S. subviolaceus in 

 which the only elytral interstices where any special elevation can be 

 detected is the seventh, but it is obviously subviolaceus all the same ; 

 and one of my examples of R. cupreus has the middle of the front of 

 the thorax quite dull on account of the confluence of the minute 

 punctulation, whilst the surface in the neighbourhood of the basal 

 angles is, with the exception of the larger series of punctures, quite 

 smooth and shining ; but such specimens as these present no difBculty 

 to an}' one acquainted with the appearance of R. subviolaceus and 

 cupreus respectively. When any of the elytral interstices are more 

 elevated than the others it is the third, fifth and seventh which are 

 affected ; not the second, fourth and sixth, as some writers have it. 



The puncturation of the thorax in all our species consists of a 

 more or less scattered series of fine punctures on a ground-work of 

 minute punctulation, and the dullness or otherwise of the surface is 

 in direct proportion to the degree of confluence of the latter ; where, 

 as in Mr. Champion's specimen of R. sodalis, this confluence is nearly 

 complete, the surface is quite dull. The tendency is for the surface 

 to be moderately shining in cupreus and subviolaceus, dull in nitens, 

 and very dull in sodalis. In fresh and clean examples the pubescence 

 is somewhat closer on the alternate interstices and the elytra con- 

 sequently have the appearance of being faintly striped. 



1 (4) Elytra with the 5th and 7th interstices (sometimes the 3rd also) distinctlj 



more elevated than the others. 



2 (3) Elytra oblong-ovate, appearing about 1^ times as long as wide... 



cupreus, Miill. 



3 (2) Elytra elongate-ovate, appearing about twice as long as wide, their sides 



evenly rounded throughout subviolaceus, Miill. 



4 (1) Elytra with onlj the 7th interstice more elevated than the others. 



