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



Genus 7Q. Hexancistra,^ Haeckel, 1881, Prodromus, p. 451. 



Definition. — C u b o s p li re r i d a with two concentric lattice -spheres and six 

 branched spines of equal size. 



The genus Hexancistra differs from its ancestral form, Hexalonche, in the 

 ramification of the six radial spines. These are very difierent in the two subgenera ; in 

 Hexancora each spine bears only three simple lateral branches, while in Hexapitys 

 there are three rows of verticillate lateral branches on each spine. 



Subgenus 1. Hexancora, Haeckel. 



Definition. — Each radial spine with three simple lateral branches only (one branch 

 from each edge of the triangular spine). 



1. Hexancistra trimspis, n. sp. (PI. 22, fig. 9). 



Cortical sliell thin walled, covered with .short conical by-spines, three times as broad as the 

 medullary shell ; its pores regular circular, three times as broad as the bars ; ten to twelve on tbe 

 radius. Pores of the medullary shell half as large, also regular circular. The two shells connected 

 by six thin prismatic radial beams, which are prolonged outside into six very stout main spines, 

 three-sided prismatic, as long as the shell diameter, with three thin wing-like edges. Each edge 

 at the distal end prolonged into a strong curved lateral branch. 



Dimensions. — Diameter of the outer shell OlS, inner 0-4 ; cortical pores O'Ol, bars O-OO." ; 

 medullary pores 0'005, bars O^OOS ; length of the six spines 013, breadth 0'02. 



Habitat— G&ntxal Pacific, Station 266, depth 2750 fathoms. 



2. Hexancistra ancorata, n. sp. 



Cortical shell thick walled, smooth, twice as broad as the medullary shell ; its pores regular 

 circular, twice as broad as the bars ; six to eight on the radius. SLx radial spmes, three-sided 

 prismatic, as long as the shell radius, with three recurved lateral branches at the distal end like the 

 three teeth of an anchor. 



Dimensions. — Diameter of the outer shell O'l, inner 0'05 ; cortical pores 0'006, bars O'OOS ; length 

 of the six spines 0-05, breadth 0'02. 



Habitat. — South Pacific, Station 296, depth 1825 fathoms. 



3. Hexancistra triserrata, n. sp. (PI. 22, fig. 10). 



Cortical shell thin walled, thorny, twice to three times as broad as the medullary shell ; the two 

 shells connected by six strong triangular beams. Inner shell spherical, with very small, regular, circular 



1 Hexancistra - Shell with six flsh-hooks ; If ayKwroa. 



