The shell is ovate or globose-conic with obtuse apex, usually perforate, thin; whorls 3,5 to 5,5- strongly convex. Aper ture truncate-rounded; peristome thin, slightly or not expanded, the columellar margin dilated and reflected. Animal viviparous, having short eye-stalks and no inferior tentacles. Jaw composed of vertical plaits with narrow intervals. Radula with tricuspid central teeth; lateral teeth tricuspid (miccyla) or with the inner cusp suppressed (dioscoricola); marginals with 4 or 5 unequal cusps; formula 14.1.14 (dioscoricola) or 15.1.15 (miccyla). Distribution, tropical and subtropical regions of both hemispheres except in arid districts and oceanic islands; living on the bark and leaves of trees and other plants. As to the systematic position of Pupisoma opinions have varied. Stoliczka and Blanford thought it a subdivision of Pupa, having in mind the larger species, lignicola and evezardi. Von Moellendorff, who knew only orcula-like species. referred it to what he considered the Fruticicolid group, in the neighborhood of Acanthinula and Zoogenites. Later estimates were less sagacious. The present writer placed it in the Endodontida, but expressed a suspicion that it might belong to Pupida. Finally Godwin-Austen placed it in the subfamily Thysanotine of the Endodontida. In restoring the genus to the Pupillide, and placing it in the subfamily Vertiginine, the writer has been influenced chiefly by the identical type of teeth and the absence of inferior tentacles. Moreover, the shell, in the type species, P. lignicola, approximates closely to such Nesopupæ as N. barrackporensis in sculpture, and is utterly unlike any Endodontid snail. The teeth of the shell of P. lignicola, such as they are, are normal for a Pupillid snail, but not like any Endodontid. The genus may be regarded as an arboreal derivative of Nesopupa, which has been modified like the Hawaiian Pronesopupæ (likewise arboreal or folicolous) by decadence or loss of teeth in the aperture, simplification of the peristome and increasing tenuity of the shell. P. dioscoricola in America and P. orcula of the Oriental fauna are so similar that transportation by commerce seems possible or even likely; yet other and strongly differentiated forms show that various species are certainly indigenous in both hemispheres. Former communication of the herds may have been around the north Pacific. Pupisoma comprises about a dozen well-established species, divided between America and the Old World. As many more doubtful or nominal species have been described by authors who knew little or nothing of previous work, or who did not compare their supposed novelties with the widespread P. dioscoricola and P. orcula. There has been no general revision of the genus hitherto, and its species have been scattered through several genera. Minute snails such as Pupillide and Vallonida frequently occupy far greater areas than the associated larger land mollusks; but there is good reason for the belief that the normal areas of some Pupisomas have been extended by commerce. Living on the bark and leaves of a great variety of shrubs. and trees, some of them such as oranges and palins, widely cultivated, these snails must often be transported to remote gardens in different parts of the world. Burnup considers the South African species to be such involuntary immigrants. Possibly the New Caledonian and Queensland forms may also be expatriated species from India or elsewhere. However, the details of distribution of Pupisoma are as yet little known in South America, tropical Africa, the East Indies, and even India. Besides the widely-spread species dioscoricola and orcula, there are various more local species in America and Asia. In America the only group which could well be thought related to Pupisoma is Bothriopupa. This genus has been placed in the Gastrocoptinæ (Vol. XXIV, p. 226), but with some doubt. If the animal proves to lack lower tentacles, as I suspect, it will be transferred to the subfamily Vertigininæ, in the neighborhood of Nesopupa. It is possible that the pitted-granulose American Pupisomas are simplified, foli- colous derivatives from a Bothriopupid ancestral stock. Observations on the living animals of these snails will bring the several hypotheses of their affinities nearer the earth. Some Thysanophoras resemble Pupisoma; yet upon going over the shells carefully there is no serious difficulty in making the distinction. P. dioscoricola, under various names, has hitherto been referred to Thysanophora or Acanthinula.