9 spp. in our area, 30 spp. total(1)
US spp.: A. arizonica
Brown 1929 [AZ-CA], A. brunnea
Casey 1889 [TX], A. conjuncta
Howden 1962 [TX], A. diminiata
Howden, 1958 [NM], A. glabrata
Cazier 1953 [sw.AZ-CA, Mexico], A. howdenorum
Warner 2011 [AZ], A. knulli
Howden 1958 [w.NM-AZ], A. mixta
Howden 1958 [AZ], A. rufula
Howden, 1958 [AZ]
Other spp. occur in Mexico and do not range into the US.
sw. US (w. TX to CA) & Mexico(1)
Appear to have generally limited, allopatric [nonoverlapping geographic areas] distributions - common in species where one or both sexes are flightless. None are evidently commonly collected. According to American Beetles, the females are still unknown, but are assumed to be flightless. Perhaps they're like Pleocoma - the females are significantly larger and usually need to be dug up, maybe they're cold adapted or found in leaf litter or detritus?
Cazier, M.A. 1953. A review of the scarab genus Acoma
(Coleoptera, Scarabaeidae). American Museum Novitates 1624: 1-13. (Full text
Howden, H.F. 1958. Species of Acoma Casey having a three-segmented antennal club (Coleoptera: Scarabaeidae). Canadian Entomologist 90(7): 377-401.
Howden, H.F. 1962. New species and synonymy in Acoma (Coloptera: Scarabaeidae). Canadian Entomologist 94(11): 1147-1155.
Howden, H.F. 1963. Speculations on some beetles, barriers, and climates during the Pleistocene and Pre-Pleistocene periods in some non-glaciated portions of North America. Systematic Zoology, 12(4): 178-201.