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



Genus 9G. Elatomma,^ n. gen. 



Definition. — A s t r o s p h ee r i d a with one medullary (intracapsular) and one 

 cortical (extracapsular) shell, the two being connected by radial beams piercing the central 

 capsule. Shell surface covered with branched radial spines. 



The oeuus Elatomma differs from Hahomma in the ramification of the radial 

 spines, and exhibits therefore the same relation to it that Cladococcus, among the 

 Coscinommida, bears to AcanthosphcBra. 



Subgenus 1. Elatommella, Haeckel. 

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



1. Elatomma jnnetuni, u. sp. 



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

 as the bars. From its surface arise twenty to thirty large, three-sided prismatic, radial spines as 

 long as the shell diameter, branched like a pine tree ; on each edge of the spine five to six ramified 

 branches, decreasing in size towards the distal end. Similar to Cladococcus plnctum. (PI. 27, figs. 1, 3), 

 but differing in the possession of a medullary shell (one-third as large as the outer), with regular, 

 circular pores, as broad as the bars. 



Dimensions. — Diameter of the outer shell 0'2. inner O^OT ; cortical pores 0'012, bars 0'004 ; 

 length of the spines 02 to 0-24. 



Habitat. — Central Pacific, Stations 266 to 272, surface. 



2. Elatomma scoparium, n. sp. 



Cortical shell thick walled, witli regular, cii'cular pores, twice as broad as the bars, connected 

 with the medullary shell by twenty thin radial beams, which are prolonged outside into twenty large 

 cylindrical radial spines somewhat longer than the radius ; in the proximal half simple, in the distal 

 half with six to nine dichotomous, irregular Ijranches. Similar to Cladococcus scoimrius (PI. 27, fig. 2), 

 but much larger, and with a large medullary shell (one-third as broad as the outer), and regular, 

 circular pores. 



Dimensions. — Diameter of the outer .shell 012, inner 0'04 , cortical pores O'Ol, bars 0-005 ; length 

 of the spines 0'08. 



Habitat. — North Pacific, Station 240, surface'. 



Subgenus 2. Elatommura, Haeckel. 

 Definition. — Pores of the cortical shell irregular, of different size or form. 



' Elatomma = Vme-eje ; iXarn. oy./m. 



