EEPORT ON THE RADIOLARIA. 545 



somewhat broader than their distal end. Patagium incomplete, connecting only the basal half of the 

 arms, with three to four concave chamber-rows, on the margin concave. (May be regarded as 

 Uuchitonia miilleri, with four arms.) 



Dimensions. — Radius of each arm 0'2, basal breadth 0'05, distal breadth O'l. 



ndbitat. — Atlantic, surface, Canary Islands. 



3. Histiastrum velatum, u. sp. (PI. 46, fig 4). 



Didtjastrum velatum, Haeckel, 1879, Atlas (pi. xlvi. fig. 4). 



Arms pear-shaped, rapidly increasing from their narrow base, nearly circular, little longer than 

 broad ; each with eight to nine transverse chamber-rows ; their lateral edges at their base concave, 

 at their end circular. Central disk with three to four rings, somewhat smaller than one arm. 

 Patagium complete, with six to seven radial beams, filling out perfectly the intervals between the 

 arms. A peculiar girdle of finer network and equal breadth surrounds the whole equatorial 

 periphery of the disk, and gives it the appearance of a square with rounded corners. 



Dimensions. — Eadius of each arm 0'2, basal breadth 0"03, distal breadth 0'12. 



Habitat. — South Atlantic, Station 330, surface. 



Subgenus 2. Histiastromma, Haeckel. 



Definition. — Distal ends of the arms sj)iny, furnished with one or more terminal 

 spines. 



4. Histiastrum quaternarium, Ehrenberg. 



Histiastrum quaternarium, Ehrenberg, 1875, Abhandl. J. k. Akad. d. Wiss. Berlin, p. 74, 

 Taf. xsiv. figs. 3, 4. 



Arms six times as long as broad at their base, with rectilinear, little divergent edges ; at their 

 truncated distal end a little broader, with one single, very strong, conical, terminal spine. Central 

 disk with four to five rings, somewhat broader than the arm. Patagium incomplete, enveloping 

 only the basal half of the arms. 



Dimensions. — Eadius of each arm 018, basal breadth 0'03, distal breadth 0'05. 



Habitat. ^¥os^\]. in the rocks of Barbados. , 



5. Histiastrum gladiatum, n. sp. 



Astromma sp.. Bury, 1862, Polycystins of Barbados, pi. v. fig. 1. 



Arms triangular, eight tunes as long as broad at their base ; at their distal end three times as 

 broad as at their base, with rectilinear, divergent edges ; their truncated end with a large conical, 

 terminal spine. Central disk with four to five rings, broader than the arms. Patagium 

 incomplete, enveloping only the basal half of the arms. 



(ZOOL. CHALL. EXP. — PART XL. — 1885.) Rr 69 



