506 THE VOYAGE OF H.M.S. CHALLENGEE. 



parallel chambered plates in the central part, and five similar plates in the peripheral part.) Pores 

 ii-regular, roimdish, tliree on the breadth of each ring. Three marginal spines long and thin, 

 cylindrical (as in Staurodidya cruciata, I'l. 42, fig. -4), longer than the diameter of the disk, and 

 half as tlrick as one ring. 



Dimensions. — Diameter of the disk (with nine rings) 0"18 ; breadth of each ring O'Ol ; 

 pores 0-002 to 0-004. 



Eahitat. — Pacific, central area, Station 263, depth 2650 fathoms. 



Genus 220. Staurodictya, Haeckel, 1881, Prodromus, p. 460. 



Definition. — P o r o d i s c i d a with four solid radial spines (commonly crossed at 

 right angles) on the margin of the circular or quadrangular disk. 



The genus Staurodictya is characterised by four marginal spines, lying opposite in 

 pairs in two crossed equatorial diameters of the disk, perpendicular one to another. 

 Sometimes the regular rectangular position of the spines becomes more or less irregular. 

 Commonly the marginal spines are the extreme prolongations of four internal crossed 

 radial beams, which are either rectilinear or zigzag-shaped. In the latter case the 

 concentric disposition of the circular rings becomes more or less spiral. Perhaps 

 Staurodictya has a near relation to the Stauralastrida (or to the Euchitonida with 

 four crossed chambered arms — Stauralastrum, Histiastrum, &c.). 



Subgenus 1. Staurodictyon , Haeckel. 



Definition. — All rings of the disk concentric (commonly ciix-ular, sometimes with 

 four incisions, produced by two crossed constrictions, or nearly square). 



1. Staurodictya medusa, n. sp. (PI. 42, fig. 3). 



All rings of the disk concentric, of nearly equal breadth, divided into four quadrants 

 by two perradial constrictions (perpendicular one to another). Pores irregular, roundish, two to 

 three on the breadth of each ring. Four marginal spines strong, pyramidal, nearly as long as the 

 radius of the disk. Margin between them denticulated. 



Diviensions. — Diameter of the disk (with four rings) 0-13 ; breadth of each ring 0-015 ; pores 

 0-002 to 0-01. 



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



2. Staurodictya ciliata, n. sja. (PI. 42, fig. 2). 



All rings of the disk concentric, of nearly equal breadth, circular or roundish, without perradial 

 constrictions. Pores subregular, circular, three to four on the breadtli of each ring. Pour marginal 



1 Staurodictya = CTOaa-net ; oTai/foV, IUtvou. 



