5. Larnacantha bicruciata, n. sp. (Pl. 50, fig. 5).
Cortical shell thorny, in the lateral plane with eight strong conical radial spines, alternating with eight smaller spines; four of the eight stronger spines opposite on the poles of the principal and transverse axes (in the figure 5, by mistake, not represented large enough), four others between those, opposite on the poles of the two crossed diagonal axes. Pores with a peculiar disposition; on both flat sides of the lentellipsis an elliptical ring of eight large elliptical pores (alternating with the eight stronger radial spines), separated by bands of smaller irregular pores. Proportion of the three axes = 2 : 3 : 4. Medullary shell nearly half as long as the cortical shell.
Dimensions.—Length of the cortical shell 0.16, breadth 0.13, height 0.08; large pores 0.03, small pores 0.003 to 0.01, bars 0.006; length of the medullary shell 0.07.
Habitat.—Indian Ocean, surface, Madagascar (Rabbe).
6. Larnacantha octacantha, n. sp.
Cortical shell thorny, with eight long and thin, cylindrical, radial spines, lying opposite in pairs in two crossed diagonal planes. Pores irregular, roundish, twice to five times as broad as the bars; about sixteen on the half meridian. Proportion of the three axes = 1 : 1⅓ : 2. Medullary shell scarcely one-fourth as long as the cortical shell. (This species resembles closely the common Tetrapyle octacantha, from which it seems to be developed by a complete over-growing of the four gates, which become closed by a network connecting the free edges of the transverse and lateral girdles.)
Dimensions.—Length of the cortical shell 0.18, breadth 0.13, height 0.1; pores 0.005 to 0.015, bars 0.003; length of the medullary shell 0.04.
Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.
7. Larnacantha cladacantha, n. sp.
Cortical shell very spiny, with eight longer ramified spines, lying opposite in pairs in two crossed diagonal planes; each spine with two to six irregular, lateral branches. Pores irregular, roundish, twice to three times as broad as the bars; about twelve on the half meridian. Proportion of the three axes = 5 : 6 : 7. Medullary shell nearly half as long as the cortical shell. (Differs from the foregoing by the branching spines end the larger medullary shell.)
Dimensions.—Length of the cortical shell 0.15, breadth 0.13, height 0.11; pores 0.01 to 0.015, bars 0.005; length of the medullary shell 0.07.
Habitat.—Indian Ocean, surface, Cocos Islands (Rabbe).
8. Larnacantha prismatica, n. sp. (Pl. 50, fig. 6).
Cortical shell smooth, four-sided prismatic, with eight short, parallel, three-sided pyramidal spines; these lie opposite in pairs in four parallel longitudinal lines, as prolongations of the four
