Two genera of Pylobotryida were incompletely described in 1860 by Ehrenberg, _Botryocyrtis_ and _Botryocampe_. We retain them here, with a stricter definition, however. Two other genera were added in my Prodromus--_Pylobotrys_ and _Phormobotrys_. {1120}The small number of species here enumerated may be easily increased, since numerous forms, belonging probably to this family, are not sufficiently known. Their study is, however, very difficult and requires accurate examination of the tiny shells from different sides. The four genera of Pylobotryida, here described, represent two different subfamilies. The terminal mouth of the abdomen remains open in the Botryocyrtida, whilst it becomes closed by a lattice-plate in the Botryocampida. There are in both groups shells with and without porous tubes; the number of these tubes, and also the number and disposition of the lobes in the cephalis, exhibits remarkable differences in the different species of those genera, and may in future serve for their division into a greater number of genera. _Synopsis of the Genera of Pylobotryida._ { Cephalis without I. Subfamily Botryocyrtida. { porous tubes, 492. _Botryocyrtis_. { Mouth of the abdomen open. { Cephalis with a { variable number of { porous tubes, 493. _Pylobotrys_. { Cephalis without II. Subfamily Botryocampida. { porous tubes, 494. _Botryocampe_. { Mouth of the abdomen closed { Cephalis with a by a lattice-plate. { variable number { of porous tubes, 495. _Phormobotrys_. Genus 492. _Botryocyrtis_,[109] Ehrenberg, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 829. _Definition._--#Pylobotryida# without tubes on the cephalis, and with the mouth of the abdomen open. The genus _Botryocyrtis_, founded by Ehrenberg upon two Indian species, is the simplest among the Pylobotryida. It may have been derived from _Botryopyle_ by the development of an abdomen (or a third shell-joint), the mouth of which remains open. 1. _Botryocyrtis serpentis_, Ehrenberg. _Botryocyrtis serpentis_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 287, Taf. x. fig. 21. Cephalis quadrilobate; the odd frontal and the two paired buccal lobes subspherical, about half as large as the odd occipital lobe. Thorax inflated, about as long as the cephalis and half as long as the ovate abdomen. Mouth of the latter constricted, of half the breadth. _Dimensions._--Length of the shell 0.12, breadth 0.06. _Habitat._--Indian Ocean (Zanzibar), depth 2200 fathoms, Pullen. {1121}2. _Botryocyrtis theocampe_, n. sp. (Pl. 96, fig. 19).