The species assigned to the genus Catillochroma are reassessed. The two characters used to characterize Catillochroma, exciple anatomy and thalline chemistry, are shown to be variable and contradictory with a number of intermediates. Consequently, Catillochroma is reduced to synonymy with Megalaria, and the species previously placed in Catillochroma transferred, or returned, to Megalaria. As such, the following new combinations are proposed: Megalaria anaglyptica, M. endochroma, M. intermiscens and M. leptocheila. The genus Lopezaria is also shown to be related to Megalaria and to be closely related to the type species of Catillochroma, C. endochroma, and so is also reduced to synonymy with Megalaria. A number of species found to have been misplaced in Catillaria are also transferred to Megalaria: M. leucochlora, M. melanopotamica, M. obludens, M. pannosa and M. phaeolomiza. Megalaria imshaugii is reduced to synonymy with M. obludens, Megalaria pannosa is reported for the first time from North America and Lopezaria isidiza is reported for the first time from outside Asia from Jamaica.
