Frontal ring kidney-shaped, nearly twice as broad as high, with a flat sagittal constriction. Sagittal ring semicircular. The four gates between the two rings are partly fenestrated by an arachnoidal network, composed of thin, irregularly branched threads, arising from the rings. The edges of all three rings are armed with irregular thorns. Basal gate circular, larger than the sagittal ring.
Dimensions.—Height of the frontal ring 0.08, breadth 0.14.
Habitat.—Indian Ocean (Madagascar), Rabbe, surface.
4. Acanthodesmia mülleri, n. sp.
Frontal ring kidney-shaped with a deep sagittal constriction. Sagittal ring ovate. The four gates between the two rings irregularly fenestrated, with a few large polygonal meshes. Edges of the rings with a few scattered thorns. Basal gate violin-shaped.
Dimensions.—Height of the frontal ring 0.1, breadth 0.16.
Habitat.—Tropical Atlantic, Station 347, surface.
Subfamily 3. Eucoronida, Haeckel, 1881, Prodromus, p. 445.
Definition.—Coronida with six large gates (four lateral and two basal gates). Skeleton composed of three rings perpendicular to one another, two of which are complete (the vertical sagittal, and the horizontal basal ring); the third is incomplete (the vertical frontal ring).