1600 THE VOYAGE OF H.M.S. CHALLENGER. 



of the branches of the radial spines. This outer shell is either a simple lattice-plate 

 (comparable to the cortical shell of Diplosphcera), or a spongy framework (as in Rhizo- 

 plegma). 



Subgenus 1. Oroplegmium, Haeckel. 



Definition. External shell a simple fenestrated lamella, forming an outer 

 concentric lattice-sphere around the inner primary shell. 



1. Oroplegma diplosphaera, n. sp. (PI. 107, fig. 1). 



Radial spines slender, cylindrical, smooth, more or less curved, about twice as broad as the 

 smooth bars of the network. External shell a simple irregular lattice-sphere, with loose polygonal 

 meshes,' which are on an average three to four times as broad as the irregular meshes of the 

 internal shell. The free prominent parts of the radial spines are irregularly branched, very long, 

 with partly confluent branches. 



Dimensions. Diameter of the inner sphere 1'5 to 2'0, of the outer 2 "5 to 3 - ; length of the 

 free spines 1'2, breadth - 04. 



Habitat. Central Pacific, Station 265, depth 2900 fathoms. 



2. Oroplegma spinulosum, n. sp. 



Radial spines slender, cylindrical, thorny, more or less curved, very similar to those of the 

 preceding species ; the shell also much resembles that of Oroplegma perplexum. It differs from the 

 latter in the more regular fenestration of both shells, and mainly in the shape of the bars and 

 the spine-branches, which are all spinulate and densely studded with small conical thorns. 



Dimensions. Diameter of the inner sphere 1'5 to 2 - 0, of the outer 2'5 to 3'0 ; length of the 

 spines 1/2, breadth 0'03. 



Habitat. Central Pacific, Station 268, depth 2900 fathoms. 



3. Oroplegma velatum, n. sp. 



Radial spines stout, cylindrical, somewhat club-shaped, spiny, slightly curved, about three to 

 four times as broad as the thorny bars of the network. External shell a simple lattice-sphere with 

 irregular polygonal meshes, which are for the most part pentagonal and about four times as broad 

 as the polygonal meshes of the inner shell. The free prominent parts of the radial spines are 

 thickened, club-shaped, and about as long as the radius. 



Dimensions. Diameter of the inner sphere2 - to 24, of the outer 2 '8 to 3'6 ; length of the 

 free spines 0'5 to 0'7, breadth 012 to 0'15. 



Habitat. Tropical Atlantic, Station 338, depth 1990 fathoms. 



