REPOET ON THE RADIOLAEIA. 261 



shells, two extracapsular or cortical shells ; the distance between the former and the 

 latter is greater than the distance between either the two inner or the two outer shells. 

 In some cases, however {e.g., Cromyomma zonaster), the distance between all four shells 

 is equal. 



Subgenus 1. Cromyommetta, Haeckel. 



Definition. — Pores of the outer cortical shell regular, of nearly equal size and 

 similar form. 



1. Cromyomma villosum, n. sp. (PI. 30, fig. 2). 



lladiul proportion of the four spheres =1:2:4:5. Outer cortical shell thick walled, densely 

 covered with innumerable bristle-shaped radial spines, half as long as the radius. Pores regular, 

 circular, double-edged, of the same breadth as the bars ; ten to twelve on the radius. The thick 

 outer shell is so dark, tliat the outlines only of the other three shells can be seen. 



Dinunswns. — Diameter of the four shells — (A) outer cortical shell 0-2, (B) inner cortical shell 

 0'16, (C) outer medullary shell 0-08, (D) inner medullary shell 0-04; pores and bars of the outer 

 shell 0-OOS ; length of the spines 0^04. 



Habitat. — Central Pacific, Station 267, depth 2700 fathoms. 



2. Cromyomma zonaster, Haeckel. 



Acanthos})hoira zonaster, Ehreuberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 285, Taf. ii. 

 fig. 2. 



Eadial projiortion of the four spheres = 2 : 3 :4 : 5. Outer cortical shell thick walled, densely 

 covered with numerous bristle-shaped radial spines, as long as the radius. Pores regular, circular, 

 twice as broad as the liars ; eight to ten on the radius. The thick outer shell is so dark, that the 

 outlines only of the other three shells can be seen. 



Dimensions. — Diameter of the four shells — (A) 015, (B) 0-12, (C) 0-09, (D) 0-06 ; pores of the 

 outer shell O'Ol, bars 0-005 ; length of the spines O^OS. 



Habitat. — Arctic Ocean, Greenland (depth 1000 fathoms), " Alert " Expedition. 



3. Cromyomma perplexum, Stohr. 



Cromyomma perplexum, Stohr, 1880, Palseontogr., vol. xxvi. p. 95, Taf. iii. fig. 5. 



Padial proportion of the four spheres = 1:2:3:4. Outer cortical sheU thick walled, densely 

 covered with short conical spines, as long as the diameter of the pores. These are regular, circular, 

 three tunes as broad as the bars ; six to eight on the radius. The thick outer shell is so dark, that 

 the outlines only of the tliree other shells can be seen. 



Dim«i,sw«.s.— Diameter of tne four sheUs — (A) 0-17, (B) 0-013, (C) 0-087, (D) 0-043 ; pores of 

 the outer shell 0-015, bars 0-005 ; length of the spines 0-02. 



^a&i^rti!.— Fossil in the Tertiary rocks of Sicily (Grotte) Stohr. 



