.REPORT ON THE RADIOLARIA. 121 



Family VII. STYLOSPH^ERIDA, Haeckel (Pis. 13-17). 



Stylosphcerida, Haeckel, 1881, Prodromus, p. 449. 



Definition. S phseroidea with two radial spines on the surface of the spherical 

 shell, opposite in one axis ; living solitary (not associated in colonies). 



The family Stylosphserida comprises a large number of very common 

 Sphseroidea, and is distinguished from all others by the possession of two radial 

 spines which are placed in one axis of the spherical shell. 1 By the expression of this 

 " main axis " as a solid rod they form the transition to the Prunoidea, in which the 

 whole shell is more or less transformed according to this " monaxial growth." But in 

 these latter the shell, as well as the central capsule, becomes ellipsoidal, prolonged in 

 one axis, whilst in the former they remain spherical. However, the distinction of 

 both nearly allied groups is sometimes difficult. 



The most simple Stylosphaerida are the Xiphostylida, with one single spherical 

 lattice-shell. To this ancestral group all other siibfamilies can be opposed as " Stylo- 

 sphserida concentrica," as their carapace is composed of two or more concentric lattice- 

 shells : two in the Sphasrostylida, three in the Amphistylida, four in the Cromyostylida, 

 five or more in the Caryostylida. In all these four subfamilies the concentric shells are 

 simple (not spongy) fenestrated spheres. In a sixth subfamily, in the Spongostylida, 

 the shell is wholly or partially composed of a spongy irregular wicker-work, with or 

 without a medullary shell in the centre. 



Both the radial spines in all Stylosphserida are opposed normally in one axis ; but in 

 many species besides the normal form occur individual abnormalities, in which the two 

 spines are not accurately opposed in this main axis, but placed in two different axes, 

 intersecting at a smaller or larger angle. In the majority of the Stylosphserida both 

 opposite spines have the same size and form ; but in some genera they are more or less 

 different, often in a very striking degree. The same differences occur in the nearly 

 allied groups of P r u n o i d e a, in the Ellipsida and Druppulida. 



The distal ends of both spines are commonly free ; but in the small group of Satur- 

 nalida (Saturnalis with one single shell, Saturmdus with two concentric shells, 

 Saturninus with three concentric shells) the distal ends of both spines are united, 

 at equal distances from the centre, by a circular or elliptical ring. This remarkable 

 peculiarity occurs in no other group of Sphseroidea, and consequently brings the 

 Saturnalida into close relation with the Discoidea. 



1 Stylospluerida = Sphaeroidea dissacantha, Prodromus, p. 449. 



(ZOOL. CHALL. EXP. PART XL. 1885.) Er 16 



