The basal plate of the cephalis, or the "cortinar plate," the "Basal-Scheibe" of Bütschli, has constantly, according to this author, two pairs of pores, an anterior smaller pair of jugular pores (the pores I of Bütschli) and a posterior larger pair of cardinal pores (the pores II in his description) (compare Pl. 95, figs. 3, 6). This applies to the majority of #Spyroidea#, but by no means to the whole group. We find basal plates with two pores only (Pl. 95, fig. 1), with three pores (figs. 2, 5), with six pores (figs. 4, 7), with nine pores (Pl. 87, fig. 2), &c. The forms with two basal pores may be derived directly from _Semantis_ (Pl. 92, figs. 1, 2); the common forms with four pores from _Semantrum_ (figs. 3-5); the rarer forms with six pores from _Semantidium_ (figs. 6, 7); and the forms with three pores from _Cortiniscus_, &c. In this as well as in other respects the variety of different forms and of developmental variations is far greater than Bütschli (1882, _loc. cit._) supposed. The bars between the pores of the basal plate possess the same value and the same names as in the Semantida (compare above, p. 954). The coryphal plate of the cephalis, its upper or apical lattice-plate, does not exhibit such important differences as the opposite basal plate, is far less variable, and is usually pierced by numerous, smaller pores. Some larger pores lie, often in pairs, on the right and left side of the sagittal constriction, and have in some groups a regular form and disposition. Either in the middle of the coryphal plate, or (usually) nearer to its dorsal margin, there arises in majority of #Spyroidea# an apical horn, directed either vertically or more or less obliquely backwards. In many #Spyroidea# three horns are developed in the coryphal plate, the odd middle apical horn and two paired frontal or lateral horns arising on each side of the latter and directed more forwards (Pl. 84, figs. 9-12). Sometimes the apical horn disappears, while the two frontal horns remain (Pl. 95, fig. 12).