REPORT ON THE RADIOLARIA. 1703 



or nearly spherical, whilst in the Circoporida it is polyaxonian, spherical or polyhedral ; 

 the hollow radial spines are arranged in the former around the main axis, in the latter 

 around the common central point. All P h se o c a 1 p i a (the Tuscarorida as well as the 

 Circoporida) are inhabitants of great depths, usually between 2000 and 3000 fathoms. 



Though the number of Tuscarorida at present known is small (only three genera, 

 with ten species), they represent a very distinct and remarkable family of Ph/EODARIA, 

 as well by their considerable size, as by the peculiar arrangement of the radial spines 

 and the structure of the shell-wall, which in some species is more solid and thicker than 

 in any other Radiolaria. The diameter of the shell is always more than 1 mm., usually 

 between 1 and 2, and sometimes more than 3 mm. 



The dry shell of the Tuscarorida is not hyaline and transparent as is usual in the 

 other Radiolaria, but perfectly opaque, milk-white or yellowish-white. This opacity is 

 caused by innumerable very fine pores, which everywhere pierce the thick, apparently 

 solid, fundamental substance of the shell-wall. Besides those very small pores, it is 

 also pierced by a certain number of larger pores, which are scattered at wide distances 

 (Narr. Chall. Exp., vol. i. pi. A, fig. 156). These larger pores or pore-channels have a 

 diameter of about O'Ol mm., and pierce the shell-wall either in a perpendicular or in 

 an oblique direction. Very numerous straight, simple, and thin needles, usually O'l to 

 0"2 mm. in length, simUar to the thin tangential needles of the Aulacanthida, are every- 

 where scattered tangentially in the cement-like fundamental substance, which seems to 

 be a peculiar carbonic silicate ; their axis is parallel to the shell-surface. 



The general form of the shell is somewhat difi'erent in the three genera of 

 Tuscarorida; ovate or spherical in Tuscarora and Tuscarusa, which bear no caudal axial 

 spine (PL 100, figs. 1—7), or sometimes three-sided pyramidal (fig. 4) ; it is sj^iudle- 

 shaped in Tuscaridium, which bears on the aboral pore an axial caudal spine (PL 100, 

 fig. 8). In every case the main axis of the shell, determining its monaxonian funda- 

 mental form, is indicated by the mouth, which is placed in the oral pole of the main 

 axis and prolonged into a short tube or proboscis. 



The hollow apophyses, arising from the shell of the Tuscarorida, are always 

 cylindrical, long and thin tubules, the narrow cavity of which communicates dii-ectly 

 with the large shell-cavity. In the axis of the tubules lies a thin axial chord or funicle, 

 composed of a few (usually three or four) sUiceous threads which arise from bridges 

 between the basal pores of the apophyses, and are twisted together like the strands of 

 a rope. The axial funicle is connected with the thin wall of the tubular apophyses by 

 innumerable very thin radial beams, perpendicular to the axis (PL 100, fig. 3a, 5h). 

 The surface of the apophyses is almost constantly covered with numerous small bristles 

 or spines, which are usually curved and directed towards theic distal ends. 



Tuscarora (PL lOO, figs. 1-6) exhibits two difi'erent groups of apophyses, which 

 may be distinguished according to their difi'erent position and direction as " circoral 



