EEPO11T ON THE RADIOLAEIA. 335 



from them in the multiplication of the cortical shell, and may be considered as the most 

 highly developed form of this amphistylous series, which proceeds from Ellipsoxiphus 

 to Litliatractus and Stylatractus. 



Subgenus 1. Cromyatractium, Haeckel. 

 Definition. Shell composed of two medullary shells and two cortical shells. 



1. Cromyatractus tetraphractus, n. sp. (PI. 15, fig. 2). 



Stylocromium tetraphractum, Haeckel, 1879, Atlas (pi. xv. fig. 2). 



Proportion of the main axes of the four concentric shells about =1:3:5:7. Network of all 

 four shells nearly of the same structure, subregular, with circular pores of equal size (in one and 

 the. same shell). The absolute size of the pores increases gradually from the innermost to the 

 outermost shell. The bars between the pores are smaller and quite smooth. Surface of the outer- 

 most shell smooth. Polar spines cylindrical, with conical apex, of variable length, nearly as broad 

 as the innermost shell. 



Dimensions. Main axes of the four shells (A) inner medullary shell O03, (B) outer medullary 

 shell 0'08, (C) inner cortical shell 015, (D) outer cortical shell 0'2 ; equatorial axes of them (A) 

 0-025, (B) 0-06, (C) 0-12, (D) 015 ; pores of (A) 0-004, (B) 0'007, (C) O'Ol, (D) 0'013, bars 0'002 

 to 0'004 ; length of the polar spines 01 to 0'3 (and more), breadth 0'015. 



Habitat. Antarctic (Indian) Ocean, Station 157, depth 1950 fathoms. 



t 



2. Cromyatractus tetralepas, n. sp. 



Proportion of the main axes of the four concentric shells about = 1:2:4:6. Network of 

 the two medullary shells regular, with small circular pores, little larger than the bars. Network of 

 the two cortical shells irregular, with much larger polygonal pores, three to nine times as broad as the 

 thin bars. (Somewhat similar to Cromyatractus ceparius, PI. 15, fig. 4.) Surface of the outermost 

 shell smooth or a little thorny. Polar spines cylindrical, very large, twice to three times as long as 

 the main axis of the outermost shell, about as broad as the innermost shell, with conical apex ; 

 smooth or a little thorny. 



. Dimensions. Main axes of the four shells (A) 0'03, (B) 0'05, (C) 013, (D) 018 ; equatorial 

 axes of them (A) 0'2, (B) 0-45, (C) Oil, (D) 014; pores of the two medullary sheUs 0'004 and 

 0-006, of both cortical shells O'Ol to OD3, bars 0'003. 



Habitat. Indian Ocean, Zanzibar, Pulleu. 2200 fathoms. 



3. Cromyatractus tetracelyphus, n. sp. (PL 15, figs. 1, la). 



Proportion of the main axes of the four concentric shells about = 1 : 3 : 10 : 11. Network 

 of the two spherical medullary shells (fig. 1) regular, with small circular pores, twice as broad as 



