158 ECHIN0DERM8 OF THE BRITISH ISLES 



well dev^elo})ed. Three or more arm spines. Only one madre- 

 porite. 



One genus, Asteronyx, known from the British seas, but 

 another, Astrodia Verrill, may be expected to occur there also, 

 the species Astrodia tenuispina Verrill having been found off 

 Spain and Portugal (42° l'-38° 5' N., ca. 12° W., 2365-3307 m. 

 " Talisman "). The characters of this genus are therefore given 

 in the key. 



Key to the genera of Aster any chidce known jrom or likely 

 to occur in the British seas. 



Disk and arms covered with skin, through which only the large 

 radial shields are seen. Arm spines (in the European species) 

 up to 8-9. Mouth papillae narrow, spiniform 



1. Asteronyx Miiller and Troschel 

 Disk and base of arms with fairly distinct, not imbricating, scales. 

 Three arm spines. Mouth papillae broad, scale-like 



Astrodia Verrill 



1. Asteronyx Miiller and Troschel. 



Disk naked, covered with a rather thick skin, through which 

 the large radial shields are more or less plainly visible. Lateral 

 plates small, forming a more or less projecting edge along the 

 lower side of the arms. Spines three or more, the lower one the 

 largest, mostly strongly club-shaped, the others shorter, more or 

 less hook-shaped. Mouth papillae small, papilliform, not broad, 

 scale-like. 



Only one species in European seas. 



1. Asteronyx Loveni Miiller and Troschel. (Fig. 90.) 

 (Syn. Asteronyx Locardi Koehler.) 



Radial shields in the shape of narrow ribs, which reach almost 

 to the middle of the disk. On dried specimens the skin is seen 

 to contain some few scattered, small plates. Dorsal plates are 

 lacking, the ventral plates are rather well developed, but irregular 

 (distinct only after removing the skin, by means of potash or 

 hyj^ochlorite of sodium). The arms are usually conspicuously 

 unequal, two or three of them being generally much longer and 

 thicker than the others. On these longer arms the lowermost 

 spine is, mainly in the middle of the arm, long and club-shajDcd, 

 thorny, and clad in a thick skin ; mostly it is directed obliquely 

 towards the ventral side of the arm. The other arm spines, 

 generally 8-9 in number, are short, hook-shaped. On the thinner 



