REPORT ON THE RADIOLARIA. 1007 



The genus Dystympanium, representing a peculiar subfamily, differs from all other 

 Tympanida in the different shape of the two parallel horizontal rings. The upper or 

 mitral ring is closed by a lattice-plate (as in Paratympanum), the lower or basal ring is 

 simple and open (as in Eutympanium). Dystympanium may therefore be regarded as 

 an intermediate form between these two genera, and may perhaps be derived from 

 Paratympanum by loss of the lower lattice-plate. 



1. Dystympanium dictyocha, n. sp. (PI. 94, figs. 15, 16). 



Basal ring circular, with eighteen to twenty short conical divergent spines. Mitral ring about 

 two-thirds as broad, hexagonal, with six ascending spines on the six corners. The latter are 

 connected with the former by six simple, straight, obliquely descending columellse, about as long as 

 the diameter of the mitral ring. Mitral lattice-plate slightly convex, with seven roundish pores 

 (six peripheral pores around a central pore). 



Dimensions. Diameter of the basal ring 0'09, mitral ring 0'06 ; length of the columellse 0'05. 



Habitat. Tropical Atlantic, Station 338, depth 1990 fathoms. 



2. Dystympanium distephanus, n. sp. 



Basal ring hexagonal, with six larger spines at the six corners, and numerous smaller ones between 

 them. Mitral ring half as broad as the basal ring, also with six angular spines. The latter are 

 connected with the former by six divergent curved columellse, about as long as the diameter of the 

 basal ring. Mitral lattice-plate flat, with irregular roundish pores. 



Dimensions. Diameter of the basal ring O'l, mitral ring O'Oo ; length of the columellse 0'09. 



Habitat. Equatorial Atlantic, Station 347, depth 2250 fathoms. 



3. Dystympanium medusa, n. sp. 



Basal ring circular, with eight larger and numerous smaller divergent spines. Mitral ring two- 

 thirds as broad as the basal ring, octagonal, with eight conical ascending spines on the eight corners. 

 The latter are connected with the former by eight divergent, curved columelke, as long as the 

 diameter of the mitral ring. Mitral lattice-plate nearly hemispherical, with nine circular pores 

 (eight peripheral pores around one central pore). 



Dimensions. Diameter of the basal ring 012, mitral ring 0'08 ; length of the columellse 0'09. 



Habitat. South Atlantic, Station 332, 'depth 2200 fathoms. 



Subfamily 4. EUTYMPANIDA, Haeckel. 



Definition. T y m p a n i d a with two simple horizontal rings, which are connected 

 by a variable number of vertical rods or columellse. Therefore the shell exhibits a large 

 simple mitral gate on the upper, and a large simple basal gate on the lower side; between 

 the two a variable number of lateral gates. 



