1556 THE VOYAGE OF H.M.S. CHALLENGER. 



5. Mesocena quadrangula, Elirenberg. 



1 Mesoeena guadrangula, Ebrenberg, 1872, Abliaiidl. d. k. Akad. d. Wiss. Berlin, pp. 145, 273. 

 1 Mesocena quafernaria, Ehrenberg, 1855, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. .302. 



Eings 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 O'Ol. 



Habitat. — North Atlantic, Faroe Channel, Gulf Stream (John Murray), depth 600 fathoms. 



6. Mesocena elliptica, Ehrenberg. 



Mesocena elliptica, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 84. 

 Mesocena ellixitica, Ehrenberg, 1854, Mikrogeol., vol. i. Taf. xx. tig. 44. 

 Dietyocha elliptica, Ehrenberg, 1872, A.bbandl. d. k. Akad. d. Wiss. Berlin, p. 44. 



Eings 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. 



Eings 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 O'OOo. 

 Habitat. — Fossil in Barbados. 



8. Mesocena hexagona, Haeckel. 



1 Mesocena senaria, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berhn, pp. 163, 273. 

 t Mesocena sepfenaria, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, pp. 163, 273. 



Eings 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 O'OOV to 001. 



Habitat. — Mediterranean, Krim (Ehrenberg), Corfu (Haeckel). 



