REPORT ON THE RADIOLARIA. 



991 



III. SubfamHy 



Dystympanida. 

 Mitral ring fenestrated, 

 basal ring simple. 



Two horizontal rings con- 

 nected by numerous (six 



IV. Subfamily 



Eutympanida. 



Two horizontal rings 

 (upper mitral ring and 

 lower basal ring) 

 simple. Apical and 

 basal parts of the 

 sagittal ring lost. 



Mitral ring closed by a lat- 



to eight or more co 

 mellaj). J 



, ' V tice-plate, basal 



simnlfl, . 



simple. 



Two horizontal rings con- 

 nected by two or three 

 columellaj (four or five 

 open gates). 



Two horizontal rings con- 

 nected by four or more 

 columellas (six or eight or 

 more open gates). 



Two columellse (parts of the 

 sagittal ring), 



Three columella; (parts of 

 the half sagittal and the 



frontal ring), 



Four colu- 

 mella. 



Six to eight 



or more 



columeUEe. 



Two rings 

 unequal, 



Two rings 

 equal, . 



Two rings 

 unequal. 



Two rings 

 equal, 



434. Dystympanium. 



435. Parastejjlianus. 



436. PrismaHiim. 



437. Pseudoeiibus. 



438. Lithocuhus. 



439. Circotympanum. 



440. Eutympanium. 



Subfamily 1. Protympanida, Haeckel. 



Definition. — T y m p a n i d a with two bisected horizontal rings, connected by the 

 complete vertical sagittal ring. (The upper mitral ring and the lower basal ring become 

 divided by the complete primary or sagittal ring into two horizontal symmetrical gates, 

 two mitral gates on the apical and two basal gates on the basal pole.) 



Genus 425. Protynipanium,^ Haeckel, 1881, Prodromus, p. 447 {sensu emend.). 



Definition. — T y m p a n i d a with two bisected horizontal rings, connected by two 

 vertical columellse. 



The genus Protympanium is the most simple form of all Tympanida, and probably 

 the common ancestral form of this family. It arises from Litliocircus by the develop- 

 ment of two horizontal rings, perpendicular to the primary sagittal ring. The upper or 

 mitral ring arises by lateral union of two pairs of superior branches, the lower or basal 

 ring by union of two pairs of basal branches of the primary vertical ring. 



1. Protympanium primordicde, n. sp. 



Mitral and apical ring of equal size, elliptical, smooth, somewhat smaller than the connecting 

 thorny sagittal ring. 



Dimensions. — Diameter of tlie two horizontal rings 0T2, of the sagittal ring 015. 

 Ecibitat. — Central Pacific, Stations 263 to 274, at various deptlis. 



1 Pro<2/™paMiM7ft= Primordial drum; •Tr^orvfi'zaiiiau. 



