A new mite genus, Gerdia (Oribatida: Damaeidae), is proposed for the North-American species Porobelba parki described by Jacot (1937). It is distinguished from Porobelba Grandjean, 1936 based on differences in prodorsum morphology, the absence of an unpaired porose area on the notogaster and the development of notogastral setae. Porobelba and Gerdia may be sister genera in a group that also includes Dameobelba Sellnick, 1929. Gerdia parki n. comb. is redescribed in detail based on numerous adults and its ontogeny is described for the first time. Eleven states (USA) and provinces (Canada) are added to its known distribution, which now encompasses a region from Manitoba to New Brunswick in the north and Missouri to North Carolina in the south.