Page:Scientific results HMS Challenger vol 18 part 2.djvu/80

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Definition.— without typical basal feet or cortinar feet.

Definition.— 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 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, and perhaps even of all  and. 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