Definition.—Semantida with two basal pores (or jugular pores), without typical basal feet.
The genus Semantis, the most primitive and the oldest of the Semantida, is of the greatest morphological interest, as the first form of Stephoidea which produces gates or pores by communicating branches, and therefore the probable ancestral form not only of this family, but of the greater number of all Stephoidea, and perhaps even of all Spyroidea and Cyrtoidea. Semantis arises from Archicircus by the production of two pairs of lateral branches from the basilar rod of the sagittal ring, one anterior pair of clavicular rods, and one posterior pair of coracal rods. By junction of the clavicular and coracal rod on each side arises a left and a right pore, the "jugular pore or jugular gate."
1. Semantis biforis, n. sp. (Pl. [92], fig. 2).
Sagittal ring obliquely ovate, nearly trapezoidal, with six pairs of short mammillated knobs or branches; dorsal rod straight, vertical, with two pairs of knobs, ventral rod strongly convex, also with two pairs of knobs; two other pairs in the apical rod. Basilar rod horizontal, straight. Basal ring with six pairs of similar knobs, three on each side. Basal gates ovate or nearly triangular.
Dimensions.—Height of the sagittal ring 0.09, breadth 0.07.
Habitat.—Central Pacific, Stations 265 to 268, depth 2700 to 2900 fathoms.
2. Semantis distoma, n. sp.
Sagittal and basal ring nearly of the same form as in the preceding species, but half as thick and armed with numerous branched spines which are about half as long as the diameter of the main gate, and with thin and curved pointed branches.
Dimensions.—Height of the sagittal ring 0.11, breadth 0.08.
Habitat.—North Pacific, Station 244, depth 2900 fathoms.