The skeleton of _Semantis_, the prototype of the Semantida, thus assumes the characteristic form of a signet-ring. The basal ring enclosing the two jugular pores corresponds to the seal-plate. It is commonly more or less horizontal; but often the apophyses descend obliquely (Pl. 92, figs. 1, 2, 13, &c.), more rarely laterally (Pl. 29, fig. 11). The further development of this typical form is essentially effected by the production of new basal pores in the horizontal seal-plate. In _Semantrum_ (Pl. 92, figs. 3, 4, 5) we find already four basal gates. Behind the jugular gates is formed a second pair, the "cardinal gates" (pores II of Bütschli). These are enclosed on the anterior margin by the coracal rods (_e_), on the posterior margin by the scapular rods (_d_), a third pair of basal apophyses, arising behind the former from the sagittal ring and uniting with them (the rods _e_2 of Bütschli). Commonly the two posterior, or cardinal gates are much larger than the two anterior, jugular gates. This characteristic basal plate of _Semantrum_, with two pairs of basal pores, is of the greatest morphological importance, as it is inherited in by far the greater number of the NASSELLARIA, though not so generally as Bütschli supposes. The basal ring of _Semantrum_ is either more circular {935}or elliptical, or more polygonal, and is connected with the basal rod of the sagittal ring by three pairs of radial apophyses, the anterior furcular, the middle coracal, and the posterior scapular rods. A third important form of Semantida is _Semantidium_ (Pl. 92, figs. 6, 7). Here we find three pairs of basal pores in the seal-plate; the third pair, newly formed, consists of the cervical gates (_e_), bounded in front by the scapular rods (_d_), behind by a fourth pair of basal apophyses, the cervical rods.