Legion IV. PHÆODARIA vel CANNOPYLEA, 1521 Order 17. Phæocystina, 1542 " 18. Phæosphæria, 1590 " 19. Phæogromia, 1642 " 20. Phæoconchia, 1710 Note on the Dimensions and Measurements, 1760 ADDENDA, 1761 ERRATA, 1763 INDEX, 1765 {889}LEGION III. NASSELLARIA, VEL MONOPYLEA, VEL MONOPYLARIA (PLS. 51-98). _Nassellaria_ (_inclusis_ Spyridinis), Ehrenberg, 1875. _Monopylea_, Hertwig, 1879. _Monopylaria_, Haeckel, 1881. _Cyrtida_ et _Acanthodesmida_, Haeckel, 1862. _Cricoidea_, Bütschli, 1882 (L. N. 40, p. 537) = NASSELLARIA. _Definition._--Radiolaria with simple membrane of the central capsule, which is monaxon or bilateral, and bears on one pole of the main axis a porous area (porochora), forming the base of a peculiar intracapsular cone (podoconus). Extracapsulum without phæodium. Skeleton siliceous, very rarely wanting. Fundamental form originally monaxon, often dipleuric or bilateral. The legion NASSELLARIA vel MONOPYLEA, in the extent here defined, was constituted in 1879 by Richard Hertwig in his work Der Organismus der Radiolarien (pp. 133-137). He gave to this large group the rank of an order, and united in it the two families Acanthodesmida and Cyrtida, which I had constituted first in 1862 in my Monograph (pp. 237, 265, 272); but he added, too, as a third family the Plagiacanthida, united by me with the former. In the first system of Ehrenberg (1847, _loc. cit._, pp. 53, 54), four families belonging to the MONOPYLEA were enumerated, the Halicalyptrina, Lithochytrina, Eucyrtidina, and Spyridina. He united the three former under the name "Polycystina solitaria," which he afterwards changed into NASSELLARIA (1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 157).