CRTNOIDEA 



23 



Only found twice, namely, 53° 58' N., 12° 24' W., 699 m. 

 ('•' Helga "), and 01° 15' N., 9° 35' W., 900 m. ('Thor "). 



Fig. 10. — Atelecrinus helga:; dorso-central, calyx, and basal part of arms. 



X 6. 



III. Family Pentametrocrinid.^ 



Free, unstalked Crinoids. Cirrus-sockets not bordered b}^ a 

 horseshoe-shaped raised rim. Basals hidden. Arms undivided, 

 5 or 10 ; when there are 10 arms {Thaumatocrinus) there are also 

 10 radials, the arms also in this case being undivided. 



Two genera represented in the N.E. Atlantic. Only one of 

 these, Pentametrocrinus A. H. Clark, is known from the British 

 seas, but very probably also the second, Thaumatocrinus P. H. 

 Carpenter, will be found there, viz. the species Th. Jungerseni 

 A. H. Clark, known from W. and S.W. of Iceland, 823-2075 m. 

 (■' Ingolf "), a small form, with ix-xvii, rarely more than xiv, 

 long and slender cirri (cf . A. H. Clark, '' Ingolf " Crinoidea, p. 13). 



Key to the genera of Pentametrocrinidce k)iown from or likely to he 



represented in the British seas. 

 5 radials and 5 undivided arms . 1. Pentametrocrinus A. H. CI. 

 10,, ,,10 ,, ,, . Thaumatocrinus P. H. Carp. 



1. Pentametrocrinus A. H. Clark. 



Five radials and 5 undivided arms. Disk large, extending 

 far up on the arms. Centro-dorsal low, cirrus-sockets not arranged 



