The Sminthuridae, which comprises the largest of the two world-wide families in the suborder Symphypleona, contains 31 genera. Four of these, Collophora, Bothriovulsus, Vesicephalus, and Temeritas are described as new. This study was undertaken mainly to more accurately ascertain relationships within the family. As a result four subfamilies, the Sminthuridinae, the Katianninae, the Dicyrtominae, and the Sminthurinae, are recognized. Of these, the Sminthuridinae seems to have been the first group to become established and the Sminthurinae was relatively the more recent group. The material has been analyzed for indications as to probable age of the units that have been called genera and the place of origin. It seems likely that the generic units existed before the close of the Cretaceous and that the group originated in the north.