REPORT ON THE RADIOLARIA. 1001 



Genus 430. Tympaniscus, 1 n. gen. 



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

 by three vertical meridional rings (or six columellae). 



The genus Tympaniscus and the following Tympanidium differ from all preceding 

 Tympanida in the multiplication of the vertical columellse, which connect the two 

 horizontal bisected rings. Tympaniscus exhibits six columellae, which may be regarded 

 as halves of three meridional rings. Only one, however, of these is complete (the sagittal 

 ring, which bisects the mitral and the basal ring) ; the two other meridional rings (placed 

 in diagonal planes) may be regarded as produced by lateral bifurcation of an incomplete 

 frontal ring ; this appears to be already foreshadowed in the preceding Octotympanum. 



I. Tympaniscus corona, n. sp. 



Basal ring larger than the mitral ring, with numerous irregular short spines but without 

 descending feet. Six columella? strongly curved, in the lower half thicker and thorny ; the four 

 lateral much thinner than the two sagittal. Apex of the jointed sagittal ring with a conical horn. 



Dimensions. Length of the shell 0'08, breadth Oil. 



Habitat. Central Pacific, Station 272, depth 2600 fathoms. 



2. Tympaniscus bipes, n. sp. 



Basal ring of about the same size as the mitral ring, with two lateral descending feet, which 

 are parallel and vertical, simple, without spur, half as long as the sagittal ring. The latter is ovate, 

 twice as long and broad as the two circular frontal rings. 



Dimensions. Breadth of the shell 0'14, length 0'09. 



Habitat. North Pacific, Station 244, depth 2900 fathoms. 



3. Tympaniscus dipodiscus, n. sp. (PL 94, figs. 5, 6). 



Basal ring smaller than the mitral ring, with two lateral descending feet, which are nearly 

 parallel and vertical, obtuse, about as long as the sagittal ring, and which bear on the outside a 

 horizontal spur. Sagittal ring hexagonal, very stout, with a caudal appendix at the base, and with a 

 small sagittal arch, bearing a stout spinulate double knob at the apex. The two subfrontal rings 

 depressed, twice as broad as high, on the outside thorny, connected at each side in the lower half 

 by a double transverse arch. 



Dimensions. Breadth of the shell 018, length 0'08 (with spines 018). 



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



1 Tympaniscus = Little drum; -rv/tirctnlijxtt;. 

 (ZOOL. CHALL. BXP. PART XL. 1886.) Rr 126 



