Definition.—Zygospyrida with six basal feet and one apical horn.
The genus Hexaspyris and the two following closely allied genera represent together the peculiar subfamily of Hexaspyrida, and differ from the other Zygospyrida in the possession of six descending basal feet; three of these are the three original, perradial, or primary basal feet of Cortina, Cortiniscus, Plagoniscus, Plectaniscus, Tripospyris, &c.; the other three, usually opposed to the former diametrically, are secondary or interradial; an odd sternal foot (opposed to the odd caudal) and two paired tergal feet (opposed to the two paired pectoral).
Subgenus 1. Hexaspyridium, Haeckel.
Definition.—Feet simple, not branched nor forked.
1. Hexaspyris alterna, n. sp.
Shell nut-shaped, smooth, with deep sagittal stricture and irregular polygonal pores; on each side of the stricture two pairs of larger square annular pores. Basal plate also with four larger collar pores. Apical horn twice as long as the shell, conical. Three primary feet (the apical and the two pectoral) slender, curved, as long as the horn; three secondary feet (the sternal and the two tergal) are half as long as the former and more highly inserted; all six feet strongly divergent, cylindrical, pointed.
Dimensions.—Shell 0.06 long, 0.09 broad; horn 0.15 long, feet 0.08 to 0.14 long.
Habitat.—Central Pacific, Stations 265 to 268, depth 2700 to 2900 fathoms.
2. Hexaspyris setigera, Haeckel.
Ceratospyris setigera, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. xx. fig. 11.