Perapion hydrolapathi (Marsham, 1802) and P. violaceum (Kirby, 1808)
These two very similar species are easiest to separate using characters used in Gonget. This uses the comparative width of the pronotum compared with the head; in violaceum broadest part of pronotum 1.43-1.76 times broader than head incross the eyes, including these. In hydrolapathi only 1.24-1.42 times broader. An underside character is a very good confirmation; in violaceum the puncturation of the 1st and 2nd abdominal segments and the metasternum is strong and quite dense, in hydrolapathi it is much finer and diffuse the disc of the metasternum being almost impunctate and somewhat striate.
P. violaceum	P. hydrolapathi
P. violaceum metasternum	P. hydrolapathi metasternum
P. violaceum	P. hydrolapathi