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



A. The Ellipsoidal Central Capsule, with one axis elongated, so that it becomes 



the vertical main axis of the body. 



a. Among the SPUMELLAEIA, Actiprunum (p. 14), Colloprunum (p. 25, PL 3, fig. 9), 



most Prunoidea (p. 288). 



b. Among the ACANTHARIA, many Amphilonchida (p. 782, PL 132, figs. 2, 6), and 



Belonaspida (p. 861). 



c Among the NASSELLAEIA, many Plectoidea (p. 905, PL 91, figs. 5, 9), 

 Stephoidea (p. 937, PL 81, fig, 16), Monocyrtida (PL 51, fig. 3), &c. 



B. The Cylindrical Central Caspule, with considerable elongation of the vertical 



main axis, which is several times as long as the horizontal transverse axis. 



a. Amongst the SPUMELLARIA, Collophidium (p. 26, PL 3, figs. 1-3) and many 



Prunoidea (Spongurus, &c.). 



b. Among the ACANTHARIA, some Amphilonchida. 



C. The Discoidal, Spheroidal, or Lenticular Central Capsule, with one axis 



shorter than the others, which becomes the vertical main axis. 



a. Among the SPUMELLARIA, Actidiscus (p. 15), Collodiscus (p. 27), and the large 



group Discoidea (p. 408). 



b. Among the ACANTHARIA, many Quadrilonchida (p. 768, PL 131), and most 



Hexalaspida (p. 874). 



c. Among the NASSELLARIA, certain Stephoidea and Cyrtoidea. 



d. Among the great legion PILEODARIA the spheroidal central capsule is almost 



always more or less flattened in the direction of the main axis (p. 1525, 



Pis. 101-128). 



D. The Lentelliptical Central Capsule (or triaxial ellipsoid), with three unequal 



but isopolar axes at right angles to each other, the sections in all three 

 dimensions of space being ellipses. 



a. Among the SPUMELLARIA, Actilarcus and the large group Larcoidea (p. 604). 



b. Among the ACANTHARIA, certain Amphilonchida and Belonaspida. 



E. The Polymorphic, Amoeboid or Irregular Central Capsule. 



a. Among the SPUMELLARIA, Collodastrum (p. 28, PL 3, figs. 4, 5), and some 

 Larcoidea. 



55. The Exometamorphic Forms of the Central Capsule. The secondary forms of 

 the central capsule, which are brought about by external causes, chiefly dependent on 

 the formation of the skeleton, are very various and in many cases devoid of special 

 interest ; in other instances, on the contrary, they are of great importance, because of the 

 clear relation of cause and effect which can be traced between the development of the 

 skeleton and of the capsule. The most important phenomena to be recorded in this 

 connection are as follows : 



