REPORT ON THE RADIOLARIA. 1005 



Genus 432. Paratympanum, 1 Haeckel, 1881, Prodromus, p. 447. 



Definition. T ympanida with two latticed horizontal rings, connected by 

 numerous descending and diverging columellse ; mitral ring smaller than the basal ring. 



The genus Paratympanum and the following nearly allied Lithotympanum form 

 together the small subfamily of Paratympanida, distinguished from the other Tympanida 

 by the fenestration of the two parallel horizontal rings. These rings in Lithotympanum 

 are both equal, whilst in Paratympanum the basal ring is larger than the mitral 

 ring ; therefore the connecting rods or columellse are in the former parallel and vertical, 

 in the latter divergent and descending. Two opposite ones of these columellse are parts 

 of the primary sagittal ring, two others are parts of the lateral or frontal ring, whilst the 

 remainder are afterwards intercalated. Paratympanum may be derived from Dystym- 

 panium by fenestration of the basal ring. 



1. Paratympanum hexastylum, n. sp. 



Six divergent columellse, about as long as the diameter of the hexagonal mitral ring, connect it 

 with the larger hexagonal basal ring. Lattice of the mitral ring hemispherical, with six roundish 

 pores, surrounding a central apical horn. Lattice of the basal ring with one large central pore, 

 surrounded by numerous peripheral pores. Eings and rods smooth, without spines. 



Dimensions. Length of the shell 0'07 ; breadth of the mitral ring 0'06, of the basal ring 0'09. 



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



2. Paratympanum octostylum, n. sp. (PI. 94, fig. 14). 



Eight divergent columellte, about as long as the diameter of the octagonal mitral ring, connect 

 it with the larger circular basal ring, and bear at each end a divergent, strong, conical spine. 

 Lattice-plate of both rings slightly convex, with numerous subregular circular pores, smooth, 

 without surface spines. 



Dimensions. Breadth of the mitral ring - 06, of the basal ring 0'09. 



Habitat. Central Pacific, Station 268, depth 2900 fathoms. 



3. Paratympanum decastylum, n. sp. 



Ten divergent columellae, only half as long as the diameter of the decagonal mitral ring, 

 connect it with the larger circular basal ring. Lattice-plate of the mitral ring nearly hemispherical 

 of the basal ring flat, both with numerous irregular roundish pores and scattered spines. Margin 

 of both rings spiny. 



Dimensions. Breadth of the mitral ring 0'08, of the basal ring O'l. 



Habitat. Central Pacific, Station 271, depth 2425 fathoms. 



1 Paratympanum = Side-drum ; x-a^ci, Tvpirxutni. 



