OPHIUROIDEA 167 



Three genera are laiown from the British seas, but two more 

 have been recorded from deep water off the Azores and might 

 thus be expected to occur also in British seas. These are Opliio- 

 geron Lyman, with the species 0. edentulus Lyman (38^ IT N., 

 27° 9' W., 1620 m., " Challenger "), and Astrogeron Verrill, with 

 the species A. supinus (Lyman) (38° 35' N., 28° 6' W., 1250 m., 

 '* Princesse Alice "). They are distinguished by the former 

 having no mouth papillae, except a single infradental papilla on 

 apex of jaw, the second by having numerous small mouth papillae 

 and a cluster of small spines on apex of jaw. The fact that the 

 two species were found at almost the same locality, however, 

 leads to the suggestion that some mistake has taken place, and 

 that the Atlantic specimen of Ophiogeron edentulus of the 

 " Challenger " were really the same as Astrogeron supinus (the 

 type of 0. edentulus Avas taken off the Fiji Islands). In the key 

 to the genera of this family, therefore, only Astrogeron is included. 



Key to the genera of OphiomyxidcB Icnown from or likely 

 to occur in British seas. 



1. Mouth papillae broad, scale-Uke, with serrate edge 



1. Ophiomyxa Miill. and Troschel 

 Mouth papillae slender, spine -like ..... 2 



2. A cluster of spines (tooth papillae) on apex of jaw . . 3 

 A single (infradental) papilla on apex of jaw;^ radial sliields 



rudimentary, without a comb of spines ; arm spines three or 

 more .... 2. Ophioscolex Miill. and Troschel 



3. Radial shields fairly well developed, with a comb of spines 



3. Ophiophrixus H. L. Clark 



Radial shields quite rudimentary, without a comb of spines. 



Arm spines 2 .... . Astrogeron Verrill 



1. Ophiomyxa Miiller and Troschel. 

 (Syn. Ophiodera Verrill.) 



Skin of disk containing numerous very fine, glassy plates. 

 Radial shields quite rudimentary. A more or less distinct series 

 of scales along margin of disk. Mouth papillae broad, scale-like, 

 with coarsely serrate edges ; teeth of the same shape. No tooth 

 papillae. 



One species is known from the British seas. Another species, 



^ Large specimens of Ophioscolex glacialis may have more than a 

 single infradental papilla, more like a cluster of spines or tooth papillae. 

 Such specimens are easily distinguished from Ophiophrixus by having 

 no spines on the radial shields (which are quite indistinct), and from 

 Astrogeron by having more than two arm spines. 



