Observations sur les Myobiidae parasites des rongeurs. Evolution parallele hotes-parasites (Acariens: Trombidiformes). - So far 52 species and 4 genera of Myobiidae have been described in rodents. Keys of genera and species are given and the subgenus Idiurobia is erected to the generic status. A complete description with figures is given of some insufficently known species. The author shows that there is a parallel evolution between the myobiids and their hosts. Ali the characters have not the same value for the evaluation of the evolution in these mites. The character of the fusion of legs I seems to be the most stable. On the basis of this character it is possible to distinguish three main groups in the myobiids: one group with all the apical segments of legs I free and well developed, this group parasitizes the marsupials; another group with the three apical segments fused, this group lives in rodents; a third group with intermediate characters and that lives in insectivores and bats. Two other characters may be utilized in the evaluation of evolution: the first is the degree of reduction of tarsal claws, the second the degree of reduction of the chaetotaxy. These two characters are however less stable and they can be utilized only into a group of hosts, e.g. to compare the evolution in genera living on different families of rodents. They are without value to compare genera living in hosts belonging to different orders of hosts.