REPORT ON THE RADIOLARIA. 1003 



Geuus 431. Tympanidium, 1 Haeckel, 1881, Prodromus, p. 447. 



Definition. T ympanida with two bisected horizontal rings, which are 

 connected by four vertical meridional rings (or eight columellse). 



The genus Tympanidium differs from all other Protympanida in the development 

 of four vertical rings, placed in four different meridional planes. Only one of these is 

 complete, the primary sagittal ring ; the three others are incomplete, inserted on the 

 two horizontal rings, which are formed by the paired mitral and basal branches of the 

 sagittal ring ; one of these three lies in the frontal plane, the two others in diagonal 

 meridional planes (between the frontal and sagittal). The shell therefore exhibits 

 twelve large gates, four of which are horizontal (the two superior mitral and the two 

 inferior basal gates) ; the eight others are vertical, separated by the eight columellse, 

 or the halves of the four meridional rings. In the subgenus Tympanomma the number 

 of gates amounts to sixteen, the four lateral gates being bisected by an incomplete 

 equatorial ring. The genus Tympanidium may be derived from Acrocubus by 

 development of the two diagonal rings (between the frontal and sagittal). 



Subgenus 1. Tympanura, Haeckel. 

 Definition. Shell with twelve gates ; the four lateral gates simple. 



1. Tympanidium foliosum, n. sp. (PL 94, fig. 1). 



Shell with twelve gates ; the four lateral gates simple. Basal gates of the shell larger than 

 the mitral gates. Sagittal ring ovate, much smaller than the three other meridional rings, which are 

 armed with numerous large elegant spines, bearing a lanceolate leaf on a thin pedicle. The 

 sagittal ring bears a bunch of similar spines only at the apex, and on both poles of the sagittal 

 axis (in the equator) a single forked spine, with two thorny branches. 



Dimensions. Length of the shell 0'09 (with spines 0'25), breadth 0'15. 



Habitat. South Pacific, Station 300, depth 1375 fathoms. 



2. Tympanidium spinosum, n. sp. 



Shell with twelve gates ; the four lateral gates simple. Basal and mitral gates of about equal 

 size. Shell similar to that of the preceding species, differing mainly in the different armature ; the 

 numerous spines, covering the convex outside of the four vertical rings, are not leaf-shaped, but 

 conical, short, of very variable size, partly simple, partly irregularly branched. 



Dimensions.- Length of the shell 0'08 (with spines 0'2), breadth 012. 



Habitat. South Pacific, Station 295, depth 1500 fathoms. 



1 Tympanidium = Small drum ; tv^xiii^iaii. 



