1. _Pylospyris denticulata_, Haeckel. _Lithopera denticulata_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 297, Taf. xii. II. fig. 7. _Lithobotrys denticulata_, Ehrenberg, 1844, Monatsber. d. Akad. Berlin, p. 203. Shell spinulate, with slight coronal and deep sagittal constriction, with irregular, roundish pores of variable size. Galea hemispherical, about half as long and broad as the nut-shaped cephalis. No symmetrically disposed larger pores. _Dimensions._--Galea 0.04 long, 0.06 broad; cephalis 0.08 long, 0.1 broad. _Habitat._--Antarctic Ocean, Ehrenberg. (Included in the ice.) 2. _Pylospyris trinacria_, Haeckel. _Spyridobotrys trinacria_, Haeckel, 1862, Monogr. d. Radiol., p. 341, Taf. xii. figs. 8, 9. Shell tuberculate, with sharp coronal and sagittal stricture. Galea campanulate, with very small circular pores, and a short conical apical horn of the same length. Cephalis nut-shaped, with large, irregular, roundish pores; two pairs of larger annular pores on each side of the sagittal ring, also four larger pores in the basal plate. _Dimensions._--Galea 0.03 long, 0.04 broad; cephalis 0.04 long, 0.07 broad. _Habitat._--Mediterranean, Messina, surface. {1084}3. _Pylospyris canariensis_, n. sp. (Pl. 95, fig. 16). Shell rough, with deep coronal and slight sagittal constriction. Galea hemispherical, with numerous small irregular, roundish pores, about half as long as the cephalis, with a slender conical horn of twice the length. Cephalis nut-shaped, with larger roundish pores of very unequal size, three pairs of larger pores on each side of the ring. Basal plate with two larger pores. _Dimensions._--Galea 0.03 long, 0.08 broad; cephalis 0.06 long, 0.11 broad. _Habitat._--North Atlantic, Canary Islands, surface. Family LIV. #PHORMOSPYRIDA#, Haeckel (_sensu emendato_) (Pl. 83, figs. 13-15; Pl. 95, figs. 17-19). _Phormospyrida_, Haeckel, 1881, Prodromus, p. 442. _Definition._--#Spyroidea# with a thorax, without galea; the shell composed of the bilocular cephalis and of a simple thorax arising from its basal face. The family #Phormospyrida# differs from the Zygospyrida, their ancestral group, in the development of a thorax, or a second fenestrated shell-joint, which arises from the lower face of the cephalis. It corresponds, therefore, to the Dicyrtida among the #Cyrtoidea#, and may perhaps be, wholly or partially, the ancestral group of the latter. When the sagittal ring and the longitudinal constriction of the cephalis disappear, the Phormospyrida pass over into the Dicyrtida. Only three species of this family have been hitherto known, which were found fossil in Barbados, and described by Ehrenberg (1875) as _Lithobotrys stiligera_ and _Petalospyris confluens_, and by Bütschli (1882) as _Petalospyris anthocyrtoides_. Fifteen other species are found in the Challenger collection, which we dispose here among five genera.