Page:Scientific results HMS Challenger vol 18 part 2.djvu/519

Rh the same length; both covered with numerous small dimples and spinules. Thorax campanulate; abdomen inversely conical; both with regular, circular pores. Thorax with nine thin curved ribs, which in the upper half of the abdomen arise as nine large feet, which are strongly compressed and curved (with the convexity outwards); their distal ends form nine ovate spinulate cones, and lie in the same horizontal plane as the basal apex of the abdomen.

Dimensions.—Length of the three joints, a 0.04, b 0.09, c 0.16; breadth, a 0.05, b 0.12, c 0.1.

Habitat.—Indian Ocean, Madagascar (Rabbe), surface.

2. Theophæna nonaria, n. sp.

Shell thorny, ovate, with two slight strictures. Length of the three joints = 1 : 4 : 5, breadth = 1 : 5 : 4. Cephalis subspherical, with a conical horn of half the length. Thorax subspherical, with regular, circular pores and conical spines. Abdomen ovate, smooth, with irregular, roundish pores. In the upper half of the thorax descend nine straight, little divergent ribs, which in the lower half become free, and represent nine slender, conical wings; their distal ends do not reach the horizontal plane in which the basal end of the abdomen lies.

Dimensions.—Length of the three joints, a 0.03, b 0.12, c 0.15; breadth, a 0.03, b 0.14, c 0.12.

Habitat.—South of Australia, Station 160, surface.

Theocorida et Theocapsida, Haeckel, 1881, Prodromus, pp. 434, 436.

Definition.— eradiata. with a three-jointed shell, divided by two transverse constrictions into cephalis, thorax, and abdomen, without radial apophyses.

The family, composed of the Theocorida and Theocapsida of my Prodromus, comprises those in which the lattice-shell is three-jointed, and bears no external radial apophyses. The two subfamilies differ in the shape of the terminal mouth, which in the Theocorida is a simple wide opening, in the Theocapsida closed by a lattice-plate. The phylogenetic origin of the Theocyrtida may be found either in the Podocyrtida or in the Sethocyrtida; they may have been derived from the former by reduction and loss of the three primary apophyses, or from the latter by development of an abdomen.

The number of species in this group is very large, and many belong to the most common and widely distributed. A great number of living and fossil species have already been described by Ehrenberg, the majority being disposed in his genera Lithocampe and Eucyrtidium.

The number of genera, however, is comparatively small, and their distinction difficult, since the form of the shell presents no striking differences.