OPHIUROIDEA 173 



Only one genus, Ophiothrix Miill. and Troschel, known from 

 the British seas, and from the North Atlantic and the JMediter- 

 ranean. Only on the African coast two more genera are repre- 

 sented, viz. Ophiotrichoides Ludwig (the species 0. Lymani 

 Ludwig, found at the Cape Verde Islands) and Ophiopteron 

 Ludwig (the species 0. atlanticum Koehler, found at the Senegal 

 coast). There is, however, hardly any prospect of finding any 

 of these genera in the British seas. (They are very easily 

 distinguished from Ophiothrix, the former by the scales of the 

 disk being entirely naked, Ophiopteron by having its arm spines 

 webbed, connected by a thin, transparent skin.) 



1. Ophiothrix Miiller and Troschel. 



Scales of disk more or less concealed by spines or thorny 

 stumps, more rarely by grains. Arm spines rather long and some- 

 what glassy, distinctly thorny ; in the distal part of arms the 

 lowermost spine is transformed into a hook. In dried specimens 

 a rather large hole is seen in the mid-line of each jaw, proximally 

 to the adoral shields. Arms very brittle. Tube -feet closely set 

 with sensory papillae. 



Two species are known from the British seas, but it is rather 

 probable that three more will prove to occur there, namely, 



0. quinquemaculata (Delle Chiaje) (syn. 0. echinata Miill. and 

 Troschel), hitherto known Avith certainty only from the Mediter- 

 ranean ; 0. maculata Ljungman (syn. Ophiothrix inducta Koehler),^ 

 known from the Josephina Bank, ca. 200 m. (" Josefina "), and 

 off the Canaries, 410 m. (" Tahsman ") ; and 0. indigna Koehler, 

 off Madeira, 150-370 m. (" Talisman "). The main distinguish- 

 ing characters of these species are given in the key, with reference 

 to the works, where full descriptions and figures are to be found. 



Key to the species of Ophiothrix known from or likely to occur 

 in the British seas. 



1. Dorsal plates of arms with the distal edge more or less produced 2 

 Dorsal plates of arms with the distal edge simply rounded , 4 



2. Middle of distal edge of dorsal plates raised into a knob, this 



giving the arms a keeled appearance .... 3 



Middle of distal edge of dorsal plates not raised, arms not keeled ; 



arms flat ; radial shields very large (" Talisman " Oph., p. 298, 



PL xix. 17-19) . . . . .0. maculata Ljungm. 



^ The author has had the type specimen of Ljungman's Ophiothrix 

 maculata for examination and finds it identical with Koeliler's 0. inducta 

 from the " Travailleur " and " Talisman " expedition. 



