11 



chamber at all. The arthrobranch on the third maxillipedes 

 is never greatly developed, and it may be absent altogether. 

 Branchial formula : — 



— VII. VIII. IX. X. XI. XII. XIII. XIV. 



Podobranchs. . ep. — ep. 1+ep. 1+ep.l+ep. l-|-ep. — 



Artlirobranchs. — — ±1 2 2 2 2 — 



Pleurobranchs.. — — — — 1 1 1 1 



Four species of Polycheles have been taken by the Helga, 

 all of them new to the British fauna. P. typhlops has been 

 taken frequently, and also several specimens of P. sculptus. 

 Three specimens of P. nanus, belonging to the variety described 

 as P. Grimaldii by Bouvier, were taken in the same haul as 

 several specimens of P. sculptus. Finally, a single specimen of 

 P. granulatus was taken. The species of this genus are good 

 examples of the very wide range so often possessed by organisms 

 living at great depths. Of the four species described here 

 P. typhlops, P. sculptus, and P. granulatus have each been found 

 in the Atlantic, Indian, and Pacific Oceans. They are nearly 

 always captured on a bottom of Globigerina ooze and their long 

 and slender chelipeds would appear to be well adapted for 

 raking and sifting the ooze in the search for food. 



A key for the separation of the four British species is given 

 below. 



A. No spines on hind border of carapace ; teeth on lateral 



margins hardly decreasing at all in size posteriorly ; 

 no ridge on the sixth abdominal tergum ; one spine on 

 the outer angle of the basal joint of the antennular 

 peduncle, . . . . . . . . . . P. granulatus. 



B. Spines on hind border of carapacs ; teeth on lateral 



margins decreasing in size posteriorly ; a double ridge 

 on the sixth tergum ; two spines on the outer angle of 

 the basal joint of the antennular peduncle. 



a. Rostral spine single ; rows of tubercles on edges 



of terga, . . . . . . . . P. typhlops, 



h. Rostral spine double ; no rows of tubercles on 

 edges of terga, 



I. Chelipeds slightly shorter than body ; ridge on 



sixth tergum very prominent, with jagged 

 edges, . . . . . . . . . . P. nanus, 



II. Chelipeds much longer than body ; ridge on 



sixth tergum low, with smooth edges, P. sculptus. 



