Key to the genus Monophylla copied from:
Schaeffer, Charles. (1911). New Coleoptera and miscellaneous notes. Journal of the New York Entomological Society, 113-126.
1. Elytra black, granulate rugose, the punctuation nearly obliterated and only visible at basal third ; prothorax unicolorous red, punctuation
coarse and dense at apical margin, fine and very sparse at middle of disk ; last antennal joint of female about as long as the four preceding
joints. ................................................................................................................................................................................................................................................ ruficollis.
Elytra distinctly punctate from base to apex. .................................................................................................................................................................................... 2.
2. Antennae of female ten-jointed. ........................................................................................................................................................................................................... 3.
Antennae of female nine-jointed. ......................................................................................................................................................................................................... 4.
3. Prothorax black, elytra brownish with a more or less distinct transverse pale spot at middle of lateral margin ; femora black, tibiae generally
pale; last joint of antennal club of female about as long as the preceding four joints. ............................................................................................. pallipes.
Prothorax red with a central black spot of variable size; elytra black with side margin in about basal half and lateral transverse spot pale,
last antennal joint of female as long or almost as long as the eight preceding joints. ......................................................................................... terminata.
4. Prothorax black with apical margin more or less reddish, elytra with lateral pale spot and sometimes with sub-apical pale sutural spot;
femora black, tibiae pale, last antennal joints of female as long or almost as long as the preceding joints. ............................................... californica.