472 THE VOYAGE OF H.M.S. CHALLENGER. 



3. Trigonactura trigonobrachia, n. sp. 



Phacoid shell two and a half times as broad as the medullary shell, with six pores on its radius, 

 without a perfect chambered girdle. Arms nearly equilateral triangular, twice as long as the diameter 

 of the phacoid shell, at the truncated distal end as broad as its diameter and three times as broad 

 as at the narrow base. (Resembles Hymenactura luxmgona, but without a patagium.) 



Dimensions. Diameter of the phacoid shell O'll, of the medullary shell 0'045 ; length of the 

 arms 0'2, basal breadth 0'035, distal breadth 01. 



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



4. Trigonactura lanceolata, n. sp. 



Phacoid shell three times as broad as the medullary shell, with eight pores on its radius, 

 surrounded by one perfect chambered ring. Arms lanceolate, three times as long as the diameter 

 of the phacoid shell, and four times as long as broad in the middle part, at both ends veiy narrow, 

 blunt. 



Dimensions. Diameter of the phacoid shell 0'09, of the medullary shell 0'03 ; length of the 

 arms 0'25, breadth in the midst 0'06. 



Habitat. South Atlantic, Station 332, depth 2200 fathoms. 



Subgenus 2. Trigonactinium, Haeckel. 

 Definition. Distal end of the arms armed with a radial spine. 



5. Trigonactura triacantha, n. sp. (PI. 38, figs. 6, 7). 



Phacoid shell two and a half times as broad as the medullary shell, with eight pores on its 

 radius, surrounded by one perfect chambered ring. Arms nearly lanceolate, in the middle part one 

 and a half times as broad as at both ends, twice as long as the phacoid shell, at the distal end 

 with a strong pyramidal terminal spine. Through the spongy framework of each arm shine 

 sixteen to eighteen transverse bars (as septa of the joints) and six to eight longitudinal piercing 

 beams. 



Dimensions. Diameter of the phacoid shell - 09, of the medullary shell 0'038 ; length of the 

 arms 0'2, greatest breadth - 08. 



Habitat. Pacific, central area, Station 265, depth 2900 fathoms. 



6. Triyonactura trigonodisciis, u. sp. 



1 Astromma sp., Bury, 1862, Polycystiiis of Barbados, Taf. xv. fig. 2. 



Phacoid shell triangular, twice as broad as the spherical medullary shell, with six to seven 

 pores^ on its radius, surrounded by one chambered ring. Arms equilateral triangular, as long as 



