230 ECHINODERMS OF THE BRITISH ISLES 



5. Arm combs of papilla?, when present, usually ^ not forming a 



continuous series across the base of arms. Edge of disk not 

 sharp ......... 6 



Arm combs forming a continuous series of papillae across base 

 of arms (rarely absent). Edge of disk usually sharp 



2. Ophiocten Liitken 



6. Ventral arm plates broadly in contact, more or less distinctly 



quadrangular. Disk high, with thick plates, among which 

 the primaries are usually very conspicuous. Arms usually 

 high and keeled ; pores large . Amphiophiura Matsum. 



Ventral plates only narrowly in contact, excepting sometimes 

 the two first, or widely separate, with a proximal angle, 

 usually more or less distinctly triangular. Disk low, scales 

 not very thick, primary plates usually not very large and 

 conspicuous. Arms usually low, somewhat flattened . 7 



7. A rather thick skin conceals the fine scaling of the dorsal side 



of disk ; no arm combs . 3. Ophiopleura Dan. and Koren 



Scales of disk not concealed by the skin. Arm combs usually 



present ......... 8 



8. Tentacle pores distinct only on the innermost 2-3 arm -joints ; 



mouth shields and usually also dorsal arm plates more or 

 less irregularly divided . . Homalophiura H. L. Clark 



Tentacle pores continuing beyond the third arm -joint 



1. Ophiura Lamarck 



9. Lateral plates of 5 proximal joints much widened, carrying 



2-3 broad, flattened spines with serrate outer edge. Five small 

 mouth papillae on each side of jaw . Ophiophycis Koehler 



Lateral plates of 2 proximal joints widened, their spines simple 

 or flattened, serrate. Only one very broad mouth papilla on 

 each side of jaw . . . Ophiomisidium Koehler 



10. Tentacle pores developed in the whole length of arm 



Ophiozonella Matsum. 

 Tentacle pores developed only on the 2-5 proximal arm -joints 



4. Ophiomusium W. Th. 



[Amphiophiura Matsumoto.] 



The four species of this genus known from the N.E. Atlantic 

 are : A. hullata (Wyv. Thomson) (Syn. Ophioglypha hullata Wyv. 

 Thomson), found in the Bay of Biscay and off the Portugal coast, 

 4165-5000 m. (" Talisman "), known elsewhere from off the 

 Bermuda Islands and from the South Atlantic, 2230-5130 m. ; 

 A. abdita (Koehler) (Syn.' Ophioglypha abdita Koehler), found at 

 12° 7' N., 33° 33' W., 6035 m. (" Princesse Alice ") ; A. convexa 



^ Only in the species Ophiura clemens Koehler the combs unite across 

 the base of arms ; but this is otherwise a typical Ophiura with very short 

 rudimentary arm spines (of. " Siboga " Ophiurids, i., PL VIII. 7-9). 



