The Scutacaridae are very little understood. Paoli divided the genera chiefly on the basis of presence or absence of ungual hooks on tarsi I and IV. This is patently a superficial and non-phylogenic character. Within a genus all grades of reduction of unguis are to be found so that it is quite conceivable that species without unguis may belong to genera with unguis. Furthermore in each genus one may find, if Paoli's figures are correct, species with dorsal segments, ranging in number from four to six. Yet number of transverse plates, usually regarded as an indication of number of somatic segments, is certainly a more fundamental character than ungual reduction. On the other hand it is quite difficult to determine with certainty the total number of transverse plates in some species. My experience leads me to regard the total number of plates as four, each bearing four bristles. At present this character will have to be disregarded.