1016 THE VOYAGE OF H.M.S. CHALLENGER. 



family of the Cyrtida, under the name Zygocyrtida, with the following definition : — 

 " Lattice-shell divided by an annular sagittal longitudinal constriction into two neigh- 

 bouring equal joints or chambers." I adopted at that time the above five genera of 

 Ehrenberg, only eight species of which were known. 



Eichard Hertwig gave in 1879 the first accurate description of the central capsule of 

 the S p y r o i d e a, and demonstrated that they possess the same characteristic structure 

 of the capsule, with a porochora and a podoconus, that is common to all Monopylea. 

 He separated the Zygocyrtida from the other Cyrtida, and united them with the 

 Stephoidea (Lithocircus) in the family Acanthodesmida. In my Prodromus 

 (1881, p. 440) I adopted that division and put the " Spyrida or Spyroidea" as a 

 separate family between the Cyrtoidea and Stephoidea. I there gave the 

 following definition : — Monopylaria gemina, testa silicea clathrata gemina, cameris binis 

 juxta compositis, annulo verticali sagittali contiguis, capsula central! a testa inclusa. 

 Promorpha dipleura vel bilaterali, dextro et sinistro antimero symmetricis, piano sagittali 

 annuloque separatis. Polum superiorem axis verticalis vel principalis plerumque spina 

 apicalis (vel occipitalis) occupat, polum inferiorem ostium clathratum (poris tribus aut 

 quatuor aut pluribus) et spina caudalis (posterior). Ad dextram et sinistram duae spinse 

 laterales distant. Ab hac forma tripoda (Monocjrrtida triradiata acuta cum annulo mediano) 

 diversse Sp5rridum formae derivandse sunt." I there divided the Spyrida into seven 

 subfamiHes and forty-eight genera. Btitschli in 1882 pubhshed accurate researches on the 

 Zygocyrtida in his Beitrage zur Kenntniss der Radiolarien-Skelete, insbesondere der 

 der Cyrtida (Zeitschr. f. wiss. ZooL, vol. xxxvi. ]). 501, Taf xxxii.). He gave a very 

 exact anatomical description of the skeleton of several fossil Spyroidea of Barbados, 

 and pointed out their close affinity to the Acanthodesmida on the one hand, and to the 

 Cyrtida on the other. Regarding their phylogenetical relation, he supjaosed that the 

 Zygocyrtida have descended from the Acanthodesmida (our Stephoidea) and are the 

 ancestors of all other Cyrtida. The best part of this valuable paper of Btitschli is his 

 exact description of the sagittal ring and its apophyses, producing the basal plate ; and 

 the general conception thus derived of the essential parts of the skeleton in all 

 MoNOPYLEA, bearing a sagittal ring. But his general conclusions were partly erroneous, 

 since the fossil Spyroidea and Cyrtoidea of Barbados, upon which they were 

 founded, contain only the minority of genera of the large groujj; and many important 

 and typical forms remained unknown to him. 



The numerous new genera discovered in the rich collection of the Challenger, and 

 mainly in the wonderful Radiolarian ooze of the Central Pacific (Stations 263 to 274) 

 throw a new light upon the complicated affinities of the whole group, and manifest a far 

 greater richness in developmental variations and admirable morphological productions than 

 Btitschli could suppose. The following description, however, must remain very incom- 

 jxlete, since the exact and thorough study of all indi"\adual forms, in the same manner as 



