REPORT ON THE RADIOLARIA. 



991 



III. Subfamily 



Dystympanida. 

 Mitral ring fenestrated, 

 basal ring simple. 



IV. Subfamily 



Eutympanida. 



Two horizontal rings 

 (upper mitral ring and 

 lower basal ring) 

 simple. Apical and 

 basal parts of the 

 sagittal ring lost. 



Two horizontal rings con- 

 nected by numerous (six 

 to eight or more colu- 

 mellse). 



Two horizontal rings con- 

 nected by two or three 

 columellae (four or five 

 open gates). 



Two horizontal rings con- 

 nected by four or more 

 columellse (six or eight or 

 more open gates). 



Mitral ring closed by a lat- 

 tice-plate, basal ring 

 simple, . 



Two columellse (parts of the 

 sagittal ring), . 



Three columellse (parts of 

 the half sagittal and the 

 frontal ring), 



Four colu- 

 mellse. 



Two rings 

 unequal, 



Two rings 

 equal, . 



f Two rings 



Six to eight | unequal, 



or more 



columellse. 1 Two rings 

 equal, . 



434. Dystympanium. 



435. Parastephanus. 



436. Prismatium. 



437. Pseudocubus, 



438. Lithocubm. 



439. Circotympanum. 



440. Eutympanium. 



Subfamily 1. PROTYMPANIDA, Haeckel. 



Definition. T ympanida 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. Protympanium, 1 Haeckel, 1881, Prodromus, p. 447 (sensu emend.}. 



Definition. T ympanida 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 Lithocircus 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 primordiale, n. sp. 



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

 thorny sagittal ring. 



Dimensions. Diameter of the two horizontal rings 0'12, of the sagittal ring 015. 

 Habitat. Central Pacific, Stations 263 to 274, at various depths. 



1 Protympanium = Primordial drum; 



