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



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

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



Dimensions. — Diameter of the disk O^OS, of the gates 0'02. 



Habitat. — Indian Ocean, Ceylon, surface, Haeckel. 



5. Triopyle renigera, n. sp. 



Disk hexagonal, five times as hroad 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 0'06, of the gates 0'02. 



Halitat. — South Paciiic, Station 295, depth 1500 fathoms. 



6. Triojji/le 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 Triocliscus sjnnosus. 



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



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



Genus 247. Triodiscus,^ 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 Triocliscus differs from the preceding Tviopyle 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 Triodiscu.s 

 correspond to certain species of Triopyle. 



1. Triodiscus lenticida, n. sp 



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

 trapezoidal, of the same size and form as the tliree gates between them, which are closed hj a loose 



^ Tiiodiscus=T)iak with three openings ; T^ioOi'aKos. 



