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



1. Pylolena inermis, n. s]?. 



Arms club-shaped, at the base half as broad, at the rounded distal end as broad as the triopyle- 

 shaped medullary shell. Surface and margin smooth. 



Diriiensions. — Diameter of the cortical shell 015, of the medullai'y shell 0"05. 



Habitat. — Equatorial Atlantic, Station 347, surface ; Central Pacific, Station 272, surface. 



2. Pylolena armata, ii. sp. (PI. 48, fig. 15). 



Arms trapezoid, at the base half as broad, at the distal end twice as broad as the triopyle- 

 shaped medullary shell. Surface and margin thorny. Twelve strong conical spines at the distal 

 end of the three arms, two opposite on both faces of the arm-edges. 



Dimensions. — Diameter of the cortical shell 0'2, of the medullary shell 0'06. 



Habitat. — South Atlantic, Station 325, surface. 



Genus 249. Hexainjle,'^ Haeckel, 1881, Prodromus, p. 464. 



Definition. — P ylodiscida with triopyle-shaped medullary shell, surrounded 

 by three distal arm-chambers. Notches between the three arms transformed into gates 

 by a connecting equatorial girdle. 



The genus Hexapyle differs from the preceding Pylolene in the development of an 

 equatorial ring or latticed girdle, which connects the free extremities of the three distal 

 ends and transforms the open notches between them into gates. It simulates therefore 

 the formation of Triopyle, from which it differs by duplication of the arm-joints and of 

 the gates (in each radius occur one proximal and one distal gate). 



1. Hexapyle triangula, u. sp. 



Cortical shell triangular, with three rounded corners, three times as broad as the triangular 

 triopyle-shaped medullary shell. Surface smooth or rough, Ijut not spiny. Three arms two-thirds 

 as broad as the three egg-shaped gates of each side. 



Dimensions. — Diameter of the cortical shell (or length of one side of the triangle) 015, of the 

 medullary shell 0'05 ; breadth of the gates 0'0(3, of the Ijridges between them 0'04. 



Habitat. — Pacific, central area. Station 272, depth 2600 fathoms. 



2. Hexapyle sexangula, n. sp. 



Cortical shell hexagonal, with six equal sides, four times as broad as the triangular triopyle- 

 shaped medullary shell. Surface rough, but not spiny. Three arms (on their smallest part) half as 

 broad as the three triangular gates (on their broadest part). 



1 IIexapyle=With six gate-openings; i^et, xi/X)). 



