The genus Holocelaeno Berlese (Acarina: Macrochelidae) is reviewed in light of several hundred collections from a variety of scarab beetle ’hosts’ and from a study of the Berlese collection in Florence, Italy. Preliminary observations on mite-beetle relationships reveal a certain degree of specificity of a given mite species for a given species of beetle. It is hypothesized that this specificity is the result of niche specialization of the beetle host, with concomitant isolation of their mite associates. Descriptions of 40 species of Holocelaeno are presented, of which 20 are listed as new. These are: Holocelaeno acinothrix, anogmos, axtelli, berlesei, brachychaeta, condyla, cosmathorax, costai, hadrosoma, hanselli, iota, jasius, melisi, neophanaei, palaeno, ritcheri, shoemakei, singeri, thyreos, and wenzeli. The following species are herein removed from the genus Macrocheles and placed in the genus H olocelaeno: dubius Evans and Hyatt (1963), floridamts Evans and Hyatt (r963), grandis Evans and Hyatt (1963), hypocrita Berlese (1917), jugulans Berlese (1917), scapularis Evans and Hyatt (1963), turki Evans and Hyatt (1963) . Holocelaeno crispa Berlese is reassigned to the genus Macrocheles. A key to species of the genus Holocelaeno is included.