right angles (already commencing in a transitional variety of Tetrapyle octacantha, J. Müller, loc. cit., Taf. ii. figs. 5, 6). Four gates transverse-elliptical, one and a half times as broad as high.
Dimensions.—Medullary shell 0.05 long, 0.04 broad; cortical shell 0.16 long, 0.13 broad; gates 0.05 high, 0.08 broad.
Habitat.—Mediterranean (Corfu), Haeckel, surface.
16. Tetrapyle pluteus, Haeckel.
Cortical shell thorny, with eight strong radial spines, lying opposite in pairs, as in the two foregoing species. On the distal edge each of the four triangular gates is protected by a prominent roof of lattice-work (or "pluteus"), which arises from the distal part of the lateral girdle and connects the two angular diagonal spines of each gate. Therefore the shell assumes the characteristic form very well represented by J. Müller in his fig. 11 (seen from the lateral side) and fig. 7 (seen from the pole of the principal axis).
Dimensions.—Medullary shell 0.04 long, 0.03 broad; cortical shell 0.15 long, 0.11 broad; gates 0.045 high, 0.07 broad.
Habitat.—Mediterranean, Atlantic, Stations 348 to 353, &c., surface.
17. Tetrapyle turrita, n. sp. (Pl. 9, fig. 10).
Cortical shell smooth, but with ten strong conical spines, two on the poles of the principal axis, eight others symmetrically distributed on both sides of the distal edge of the four roundish gates, and directed towards the transverse axis. Lateral girdle lanceolate, twice as long as broad.
Dimensions.—Medullary shell 0.05 long, 0.04 broad; cortical shell 0.2 long, 0.1 broad; gates 0.05 high, 0.07 broad.
Habitat.—Pacific, central area, Station 274, depth 2750 fathoms.
18. Tetrapyle dodecaceros, n. sp.
Cortical shell thorny, with twelve stronger conical spines, eight diagonal spines in two crossed planes (as in Tetrapyle octacantha), and four others in the lateral plane, in pairs on both sides of a deep sagittal constriction of the quadrangular lateral girdle. Four gates kidney-shaped, twice as broad as high. On each half wing of the transverse girdle five to six longitudinal rows of irregular, roundish pores.
Dimensions.—Medullary shell 0.06 long, 0.04 broad; cortical shell 0.18 long, 0.14 broad; gates 0.04 high, 0.08 broad.
Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.
