In summary two new species of demodicids, D. longissimus and D. molossi, have been described for all life cycle stages. They are unusually large, remarkably modified species both of which are restricted to the Meibomian ducts of their respective hasts, Carollia perspicillata and Molossus molossus. Both are also low grade pathogens subsisting primarily on epithelial cells of the ducts. The major adaptations are apparently primarily related, as holdfast mechanisms, for maintenance of position in ducts which are sluiceways for the Meibomian secretions. Both species also possess operculate ova, and larval egg teeth - the first report of such structures for the genus. The differences between the two species, such as larger girth and more prominent holdfast structures in D. molossi, are thought to be directly related to the difference in physical dimensions of the ducts of the two hosts, that of Molossus molossus being nearly two times the diameter of the Meibomian duct of Carollia perspicillata. Sorne information is also provided on the population structure of D. longissimus and D. molossi. The ratio of immatures to adults is very similar in both (3:2; 4:3) as is also the sex ratio (1:2 vs 2:3).