REPORT ON THE RADIOLARIA. 971 



fore be regarded as the common ancestral form of this family. The simple skeleton 

 is composed of two meridional rings only, perpendicular one to another a sagittal and 

 a frontal ring. 



Subgenus 1. Zygostephus, Haeckel, 1881, Prodromus, p. 446. 



Definition. The two vertical rings of nearly equal height, therefore without 

 sagittal constriction. 



1. Zygostephanus dissocircus, n. sp. (PI. 93, fig. 1). 



Both rings elliptical, of nearly equal height, smooth, without spines. Frontal ring somewhat 

 longer than the sagittal. No sagittal constriction. 



Dimensions. Height of the rings 0'07, breadth O'l. 



Habitat. Cosmopolitan; Mediterranean, Atlantic, Pacific, surface. 



2. Zygostephanus serratus, n. sp. 



Both rings elliptical, of nearly equal height, with a serrate prominent edge on the outer 

 convexity (in the transverse section three-edged). No sagittal constriction. 

 Dimensions. Height of the rings 0'08, breadth 012. 

 Habitat. Central Pacific, Station 266, depth 2750 fathoms. 



3. Zygostephanus miilleri, Haeekel. 



Zygostephanus miilleri, Haeckel, 1862, Monogr. d. Radiol., p. 268, Taf. xii. fig. 2. 



Both rings elliptical, of nearly equal height, armed with numerous (about fifty) slender curved 

 spines, as long as the radius of the rings ; commonly each ring with twelve pairs of divergent spines. 

 No sagittal constriction. 



Dimensions. Height of the rings 0'06, breadth O'l. 



Habitat. Mediterranean (Messina), surface. 



4. Zygostephanus ratnosus, n. sp. 



Both rings elliptical, of nearly equal height, armed with numerous branched spines, which are 

 arranged on each ring in two divergent rows ; the branches of the spines are curved and partly 

 protect the open gates. No sagittal constriction. 



Dimensions. Height of the rings 0'07, breadth 0'09. 



Habitat. North Pacific, Station 244, depth 2900 fathoms. 



