1. Larnacantha dissacantha, n. sp.
Cortical shell smooth, with two large cylindrical spines, opposite on the poles of the principal axis, and somewhat longer than it. Pores regular, circular, three times as broad as the bars; about eleven on the half meridian. Proportion of the three axes = 2 : 3 : 4. Medullary shell one-third as large as the cortical shell.
Dimensions.—Length of the cortical shell (principal axis) 0.13, breadth (transverse axis) 0.1, height (sagittal axis) 0.07; pores 0.009, bars 0.003; length of the Larnacilla-shaped medullary shell 0.045.
Habitat.—North Pacific, Station 256, depth 2950 fathoms.
2. Larnacantha stauracantha, n. sp.
Cortical shell smooth, with four large conical spines in the lateral plane, two larger opposite on the poles of the principal, two smaller on those of the transverse axis. Pores regular, circular, twice as broad as the bars; about seventeen on the half meridian. Proportion of the three axes = 3 : 3.5 : 4. Medullary shell one-third as large as the cortical shell.
Dimensions.—Length of the cortical shell 0.15, breadth 0.13, height 0.11; pores 0.008, bars 0.004; length of the medullary shell 0.05.
Habitat.—Pacific, central area, Station 274, surface.
3. Larnacantha quadricornis, n. sp.
Cortical shell spiny, with four strong, horn-like curved spines in the lateral plane, opposite in pairs on the poles of the crossed diagonal axes. Pores irregular, roundish, twice to four times as broad as the bars; about fourteen on the half meridian. Proportion of the three axes = 2 : 3 : 4. Medullary shell one-third as large as the cortical shell.
Dimensions.—Length of the cortical shell 0.14, breadth 0.11, height 0.07; pores 0.006 to 0.012, bars 0.003; length of the medullary shell 0.05.
Habitat.—Pacific, central area, Station 270, surface.
4. Larnacantha hexacantha, n. sp. (Pl. 50, fig. 4).
Cortical shell thorny, with six strong conical radial spines in the lateral plane, two opposite on the poles of the principal axis, four others opposite in pairs on the poles of the two crossed diagonal axes. Pores with peculiar distribution; twelve large elliptical pores (nearly of the size of the medullary shell) symmetrically disposed in four crossed meridians (between the sagittal and the lateral meridians), separated by bands of smaller irregular pores. Proportion of the three axes = 3 : 4 : 5. Medullary shell hexagonal, one-third as large as the cortical shell.
Dimensions.—Length of the cortical shell 0.14, breadth 0.11, height 0.08; large pores 0.04, small pores 0.003 to 0.01, bars 0.004; length of the medullary shell 0.05.
Habitat.—Pacific, central area, Station 263, depth 2650 fathoms.
