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



three heart-shaped gates. On the six corners of the margin (which forms a regular hexagon) are 

 six pyramidal radial spines, as prolongations of the arm-edges. 



Dimensions. Diameter of the disk 0'05, of the gates 0'02. 



Habitat. Indian Ocean, Ceylon, surface, Haeckel. 



5. Triopyle renigera, n. sp. 



Disk hexagonal, five times as broad as the circular central chamber. Three arm-chambers 

 trapezoidal, at the base one-third, at the distal end two-thirds as broad as the three kidney-shaped 

 gates. On the six corners of the margin (which forms an irregular hexagon) six conical radial 

 spines, as prolongations of the arm-edges. 



Dimensions. Diameter of the disk O06, of the gates 0'02. 



Habitat. South Pacific, Station 295, depth 1500 fathoms. 



6. Triopyle spinigera, n. sp. 



Disk roundish, triangular, four times as broad as the triangular central chamber, which is armed 

 with three radial spines between the arms. Arm-chambers club-shaped, at the narrow base one- 

 fourth, at the distal end half as broad as the square gates. On the margin twelve large conical 

 spines, two opposite on each face of the distal end of each arm-edge. Three smaller radial spines 

 on the three corners of the girdle (in the same interradial meridian planes as the three spines of the 

 central chamber). Compare Triodiscus spinosus. 



Dimensions. Diameter of the disk 0'05, of the gates 0'02. 



Habitat. South Atlantic, Station 332, depth 2200 fathoms. 



Genus 247. Triodiscus, 1 n. sp. 



Definition. P ylodiscida with a simple, spherical or lenticular, central chamber, 

 surrounded by three simple arm-chambers. Notches between the three arms closed by 

 lattice -work and by an equatorial girdle. 



The genus Triodiscus differs from the preceding Triopyle in the development of loose 

 lattice-work on both sides of the discoidal shell. This network closes the gates and 

 transforms the whole shell into a fenestrated lens. The singular species of Triodiscus 

 correspond to certain species of Triopyle. 



' 1. Triodiscus lenticula, n. sp 



Disk circular, lenticular, three times as broad as the central chamber. Three arm-chambers 

 trapezoidal, of the same size 'and form as the three gates between them, which are closed by a loose 



1 JVioeKscs=Disk with three openings ; 



