We have a lot of flats from Meghalaya that need your expert views for proper identification. I put my hands on their ids but most of my ids are tentative and need your confirmation.
Key as followingt Evans.
1a, 1b, 12a, 19a ...FW ce3llspot is nearer apex than base., 19b, 19c , 21 (19d) HW cilia narrowly white or brown; FW spot 3 conjoined to band ; only outer spot in space 1b...C. nigricans.
Note this individual match key line 19a well, ie FW cellspot is nearer FW apex than base.
C. affinis. FW 20mm. FW band irregular with a tornal spot in space 1b.
Antennal club narrowly banded yellow at base & HW cilia narrowly chequered yellow. http://yutaka.it-n.jp/hes/90520010.html
C. andamanicus hanna. Like affinis but much smaller FW 17mm. FW band irregular broad in the middle & HW cilia plain ( may be vaguely chequered). http://yutaka.it-n.jp/hes/90530010.html
Thank you so much for such a nice review with lot of valuable information. C. affinis is very new to me. I am sure we might have come across C. andamanicus hanna but might have overlooked it for C. aurivittata. But I hope from next time I will observe them carefully in the field knowing there are so many similar looking ones.
And really much love and greeting from India (North-East) to you Seow sir. Whatever you are doing in this forum is incomparable and most importantly you are doing it selflessly.
I wish my school teachers would have been like you (on a lighter note).