5. Mesocena quadrangula, Ehrenberg.
Rings square, with four radial spines on the corners of the square. Ehrenberg has given only the name of this species, but neither diagnosis nor figure. I think it may be identical with the species described, which I found in the North Atlantic.
Dimensions.—Diameter of the rings 0.02 to 0.025, length of the spines 0.007 to 0.01.
Habitat.—North Atlantic, Færöe Channel, Gulf Stream (John Murray), depth 600 fathoms.
6. Mesocena elliptica, Ehrenberg.
Mesocena elliptica, Ehrenberg, 1854, Mikrogeol., vol. i. Taf. xx. fig. 44.
Dictyocha elliptica, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 44.Rings elliptical or ovate, with four peripheral spines which lie in two diameters, perpendicular to one another, two opposite in the major, the two others in the minor axis of the ellipse.
Dimensions.—Diameter of the rings 0.015 to 0.03, length of the spines 0.005.
Habitat.—Fossil in Tertiary rocks of the Mediterranean (Placca di furni, from Zante, Greece); Caltanisetta, Sicily.
7. Mesocena pentagona, n. sp.
Rings regularly pentagonal, with smooth straight bars, and with five short and straight radial spines on the five corners.
Dimensions.—Diameter of the rings 0.02, length of the spines 0.005.
Habitat.—Fossil in Barbados.
8. Mesocena hexagona, Haeckel.
Rings regular, hexagonal, with six radial spines on the six corners (sometimes between the usual six-radiate rings of one and the same individual are intermingled single rings with five or seven spines).
Dimensions.—Diameter of the rings 0.025 to 0.03, length of the spines 0.007 to 0.01.
Habitat.—Mediterranean, Krim (Ehrenberg), Corfu (Haeckel).
