Each pileated piece of the skeleton stirrup-shaped, with four paired meshes similar to the hats of Dictyocha fibula, but distinguished by four small centripetal thorns, which start from the inside of the basal ring, at the side of the four ascending beams. No apical spine.
Dimensions.—Diameter of the basal ring 0.03, of the meshes 0.01.
Habitat.—Fossil in Tertiary rocks of North America (Miocene Tripel of Richmond, Virginia, &c.).
11. Dictyocha stapedia, n. sp. (Pl. [101], figs. 10-12).
Each pileated piece of the skeleton stirrup-shaped, with four paired meshes, similar to the hats of Dictyocha fibula and Dictyocha messanensis, but distinguished by four small centripetal teeth, which start from the inside of the basal ring, at the side of the four ascending beams. In the centre of the diagonal arch arises a vertical apical spine (differing from Dictyocha epiodon). This species seems to be the most common of the living forms and widely distributed over all warmer seas. I observed in Ceylon, taken on the surface, the living specimen figured in Pl. [101], fig. 10, the numerous spicula were irregularly scattered over the spherical surface of the alveolate calymma. Other specimens occur in various preparations of the Challenger collection, from the Atlantic and the Pacific. The majority of the siliceous little hats exhibited the stirrup-form shown in fig. 11, and many were united in pairs, forming a twin-piece (fig. 12). Intermingled with these are found some irregular forms, representing the specific form of some allied species, viz., Dictyocha speculum, Dictyocha staurodon, Dictyocha epiodon and Dictyocha messanensis.
Dimensions.—Diameter of the basal ring 0.015 to 0.03, of the meshes 0.005 to 0.012.
Habitat.—Cosmopolitan; Atlantic, Pacific, Indian Ocean, in the Tropical and warmer regions; Stations 159, 244, 266-272, 318, 352, &c.
12. Dictyocha rhombus, n. sp.
Each pileated piece of the skeleton stirrup-shaped, similar to Dictyocha stapedia, with four paired meshes. It differs from the latter in the rhomboid form of the basal ring and the larger size of the two opposite meshes, which are two to three times as large as the two others. Therefore the four centripetal teeth of the basal ring do not stand in the four single meshes, but in pairs only in the two larger meshes.
Dimensions.—Diameter of the basal ring 0.02, of the meshes 0.005 to 0.01.