REPORT ON THE RADIOLARIA. 



1129 



B. The radial structure, indieaterl by radial apophyses arising from the rIicU, offers 

 three principal diiferenccs, according to which the whole group of C y r t o i d e a may 

 be divided into three large groups or sections, viz., (l) Pilocyrtida, or Cyrtoidea 

 triradiata, with three radial apophyses ; (2) Astrocyrtida, or Cyrtoidea multiradiata, 

 with numerous radial apophyses (four to nine or more) ; and (3) Coroc5^rtida, or 

 Cyrtoidea eradiata, without external radial apophyses. The majority of Cyrtoidea 

 are Pilocyrtida, with three radial apophyses, which are probably homologous to the three 

 primary feet of the Plcctoidea and of Cortina (therefore " cortiuar feet "). The 

 Astrocyrtida, or the Cyrtoidea with a variable number of radial apophyses (at least 

 four to six) may be derived from the Pilocyrtida by interpolation of secondary or 

 interradial apophyses between the three primary or perradial apophyses. The 

 Corocyrtida, however, or the Cyrtoidea without external radial apophyses, may have 

 originated by reduction and loss of the latter, either from the Pilocyrtida or from the 

 Astrocyrtida. 



C. The shape of the basal mouth in the Cyrtoidea exhibits two essential 

 diflferences only, viz., (l) the terminal mouth of the shell is a simple wide opening in 

 the Stomocyrtida, or (2) the terminal mouth is closed by a lattice-plate, in the 

 Clistocyrtida. As these two different cases occur in all the twelve families, which we 

 have distinguished according to the differences in the number of joints and in the 

 radial structure, we get altogether twenty-four subfamilies which are synoptically 

 arranged in the following table : — 



(ZOOL. CHALL. EXP. — PAET XL. 1886.) 



Er 142 



