ECHINOIDEA 343 



In British seas this species has been found only once (one 

 specimen), at 61° 15' N., 9° 35' W., 900 m. (' Thor "). It is 

 only known elsewhere from Denmark Strait and off S.W. Iceland, 

 873-2340 m. (" Ingolf "). 



II. Family Pourtalesiid^. 



Mouth placed vertically at the end of a deep oral invagination. 

 Second plate of the anterior paired interambulacra paired, the 

 two plates of this number being placed side by side (" amphi- 

 placous " ) . Pores all simple . Apical system usually disconnected . 

 A subanal fasciole usually present. Shape of test very diversified, 

 often very elongate, more or less bottle-shaped. 



Two genera are represented in the British (and N.E. Atlantic) 

 seas. 



Key to the genera of Pourtalesiidce of the British seas. 

 Not very slender forms ; posterior paired bivial ambulacra discon- 

 nected (Fig. 204, 1) . . . 1. Pourtalesia A. Ag. 

 Very slender forms ; posterior paired bivial ambulacra continuous 

 (Fig. 204, 2) .... 2. Echinosigra Mrtsn. 



1 2 



Fig. 204. — Outline figures for showing the plate arrangement of the ventral 

 side (the bivium) in Pourtalesia Jeffreysi (1) and Echinosigra phiale (2). 

 It is seen that the plates of the bivial ambulacra (punctated) are dis- 

 connected in Pourtalesia, while in Echinosigra they are contiguous. 

 (After Loven, On Pourtalesia (1), and Th. Mortensen, ''Ingolf 

 Ech., ii.) 



st. Sternum ; 1, Labnim. 



