384 EOHINODERMS OF THE BRITISH ISLES 



Key to the species of Bathyplotes known from or likely 

 to occur in the Briiish seas. 



1. Tube-feet of latere -ventral ambulacra very large ; mid-ventral 



radius with very numerous small tube -feet, covering the whole 

 space between the two lateral series of large tube -feet 

 {''Monaco'', Ixvi., p. 34, PI. V. 8) . B. Pourtalesii (Theel) 



Tube-feet of latero -ventral ambulacra not very large ; mid- 

 ventral radius usually naked, sometimes with a variable number 

 of tube -feet like those of the lateral series ... 2 



2. A series of small papillae between the latero-ventral tube-feet and 



the marginal fringe, mainly in the posterior half of the body 

 (" Talisman " Holoth., p. 332, Pis. XII. 3-4, XVIII. 1-9) 



B. reptans Perr. 



The space between the latero-ventral tube-feet and the marginal 



fringe without small papillae . . I. B. natans (M. Sars) 



I. Bathyplotes natans (M. Sars). (Fig. 228, 2.) 



(Syn. Stichopus 7tatans M. Sars ; Stichopus Tizardi Theel ; 

 Bathyplotes fallax Ostergren.) 



Tentacles 20 in the adult, fewer in younger specimens. Tube- 

 feet of the latero-ventral ambulacra in a double series, or more. 



Fig. 228. — 1. Stichopus tremidus, side view. 2. Bathj/plotes natans, dorsal 

 side. 3. Mesothuria intestinalis, side view. All reduced. (From 

 Danmark's Fauna.) 



well developed, but not unusually large ; the mid-ventral radius 

 usually entirely naked, but sometimes a few^ scattered tube-feet 



