90 ECHINODERMS OF THE BRITISH ISLES 



Greenland, and Spitz bergen, 520-2700 m., may well be expected 

 to occur also in the cold area of the Faroe Channel, and is there- 

 fore included in the key. 



Key to the genera of Poraniidce known from or likely to occur 

 in the British seas. 



1. Dorsal side entirely devoid of a skeleton but set with fine spines. 



Oral interradial areas with small plates in isolated transverse 

 series, and with spines in transverse series, parallel to the 

 spines of the lower marginals . Tylaster Dan. and Koren 



Dorsal side with skeletal plates, oral interradial plates not arranged 

 in isolated transverse series ...... 2 



2. Dorsal side with isolated, conical spines 3. Marginaster Perrier 

 Dorsal side naked, or with a close coat of microscopical spines, 



or with grains ........ 3 



3. Dorsal side naked ; spines on the lower marginal plates rather 



coarse, forming a distinct fringe along the edge of the disk 



1. Porania Gray 



Dorsal side with grains or with a close covering of microscopical 



spines.^ The spines of lower marginal plates fine, only indistinctly 



forming a fringe along the edge of the disk, or are wholly 



wanting ... 2. Poraniomorpha Dan. and Koren 



I. Porania Gray 



Disk large, convex ; rays short, but distinct. Dorsal side 

 covered with a thick, naked skin, entirely without spines. Lower 

 marginals with 3-5 fairly strong spines, forming a fairl}^ distinct 

 fringe along the edge of the body. 



Only one species in British (and Euroj^ean) seas. 



L Porania pulvillus (O.Fr.MiXWev). (Fig. 51.) 



(Syn. Asteropsis pulvillus (0. Fr. Miiller) ; Goniaster 

 Templetoni Forbes.) 



Dorsal surface smooth and greasy to the touch, the only 

 processes on it being the scattered groups of papulae. When 

 dried the dorsal skeleton can be discerned through the skin. 

 Upper marginal plates naked, narrow, leaving between their 

 lower ends a space in which papulae may occur. Oral inter- 

 radial area naked, often with distinct radiating furrows. Ambul- 



^ As these fine spines are enclosed in thick skin, it is not easily seen 

 directly whether the skin is really or only apparently naked, and it may be 

 necessary to examine a small piece of the skin microscopically in order to 

 ascertain whether spines are present or not. In dried specimens the spines 

 are easily discerned with a lens. 



