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



the central capsule) with the outer, extracapsular, cortical 8hell. But in some species 

 only one medullary shell is enclosed in the central capsule, whilst both other shells lie 

 outside it. In such case the distance between these two cortical shells is much smaller 

 than their distance from the simple internal medullary shell. These forms correspond 

 more to aculeate Rhodosjihcerce, whilst the others resemble aculeate TJiecosphcerce. 



Subgenus 1. Actinommantha, Haeckel. 



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

 form ; spines on the entire surface (commonly one spine at each nodal-point). 



1. Actinomma hexagonium, n. sp. 



Cortical shell, as well as both medullary shells, very thin walled, with regular, hexagonal pores 

 and thread-like bars between them. Pores of the outer shell twice as broad as those of the middle, 

 and three times as broad as those of the inner shells. Radial proportion of the three spheres = 

 1 : .3 : 9 ; about twenty thin radial beams between them. At each nodal-point of the surface arises 

 one bristle-shaped radial spine, half as long as the radius. 



Dimensions. — Diameter of the outer shell 0-22, middle 0'07, inner 0'02.5 ; meshes of the cortical 

 shell O'Ol ; length of the spines 0'05. 



Habitat. — Central Pacific, Stations 270 to 274, .surface. 



2. Actinomma facetum, n. sp. 



Cortical shell thick walled, with regular, circular, hexagonally framed pores, three times as 

 broad as the bars. Pores of both medullary shells regular, circular. Eadial proportion of the three 

 spheres = 1:2:4; about forty thin radial beams between them. At each nodal-point of the surface 

 arises one short, three-sided pyramidal, radial spine, about one-third as long as the rachus. 



Dimensions. — Diameter of the outer shell 0'16, middle 0"08, inner 0'04; cortical pores 0'012, 

 bars 0'004 ; length of the spines 0"03, basal breadth O'OIS. 



Hahitat. — North Pacific, Station 253, depth 3125 fathoms. 



3. Actinomma anthomma, n. sp. 



Cortical shell thick walled, with regular, six-lobed pores, twice as broad as the bars. At each 

 nodal-point of the surface is one short conical radial spine, as long as the diameter of the pores; 

 one corresponding to each lobe, and there is therefore around each j)ore a regular corona of six spines, 

 as in Haliomma lirianthus (PI. 28, fig. \h). Both medullary shells with simple, circular, regular 

 pores. Radial proportion of the three spheres = 1 : 2'5 : 7 ; radial beams between them only six, 

 opposite in pairs in the three dimensive axes. 



