Habitat.—North Atlantic, Station 354, surface.
Genus 592. Podocyrtis,[[209]] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.
Definition.—Theopilida (vel Tricyrtida triradiata aperta) with three simple, terminal feet on the mouth of the abdomen, without lateral ribs or wings. Apex with a horn, which usually is simple.
The genus Podocyrtis, and the two following closely allied genera, differ from all the preceding Theopilida in the absence of lateral ribs or wings, and the possession of three free terminal feet, which arise directly from the peristome, or from the margin of the abdominal mouth. They may be derived from Pleuropodium by reduction and loss of the three piercing lateral ribs, the terminal free prolongations of which only remain. The genus Podocyrtis is one of the largest and most common among all Cyrtoidea, being rich mainly in fossil forms. Ehrenberg in his Polycystins of Barbados (1875, loc. cit., p. 80) enumerated not less than thirty-one species. Some of these are yet living, and occur in the Pacific Radiolarian ooze collected by the Challenger. Other new forms are to be added, so that the number of species described in the following pages amounts to forty-five. Many of these are cosmopolitan, or at least common and widely distributed. To facilitate study we may divide this large genus into four subgenera: in two of these the terminal feet are divergent, or nearly parallel; in the two others convergent. In each of these two groups the pores of the thorax and the abdomen are either nearly equal in size and form, or distinctly different, the abdominal pores being often much larger than the thoracic. The small cephalis bears constantly an apical horn, which is usually simple, rarely branched.
Subgenus 1. Podocyrtarium, Haeckel.
Definition.—Feet divergent (the distance between their ends being greater than that between their bases). Pores of the thorax and abdomen nearly equal in size and similar in form.
1. Podocyrtis tripodiscus, n. sp. (Pl. [72], fig. 4).
Shell nearly conical, gradually dilated from the apical to the basal part, with two slight strictures. Surface a little rough. Length of the three joints = 1 : 2 : 4, breadth = 2 : 4 : 6. Pores subregular, circular, quincuncially disposed, of nearly equal size in the conical thorax and the subspherical abdomen. Cephalis hemispherical, with smaller pores and a spindle-shaped spiny horn of twice the length. Feet cylindrical, as long as the abdomen, little divergent, their ends curved outwards and thickened into a papillate knob.
Dimensions.—Length of the three joints, a 0.02, b 0.03, c 0.08; breadth, a 0.03, b 0.07, c 0.11.
Habitat.—Central Pacific, Station 265 to 272, depth 2425 to 2925 fathoms.