280 



ECHIN0DER.M8 OF THE BRTTT8H ISLES 



Only one species kno\Mi from the British seas (and the N.E, 

 Atlantic). 



1. Phormo.'^mna 2^l<^tcentaWyY. Thomson. (Fig. 157.) 



On the oral side of test each interambulacral plate carries 

 2-3 very large and deep areoles, occupying nearly the whole 

 plate ; the ainbiilacral plates carry only one such large areole each. 

 The tubercles small in comparison with their large areoles ; it 

 is the spines attached to these tubercles and areoles which are 

 club-shaped, clad in a bag of skin. Along the edge of the test 

 there is a more or less marked fringe of smaller, close-set spines. 

 The aboral side of the test is sparsely covered with spines, the 



Fig. 15: 



-Phormosoina placenta ; oral (1) and dorsal side (2). About Juilf 

 size. (After Wyv. Thomson, " Porcupine " Ech.) 



tubercles not surrounded by large areoles, and the spines not 

 club-shaped, nor enclosed in a skin-bag. Tridentate pedicellarise 

 simple, leaf-shaped. Colour in life appears to be purplish below, 

 grey above, flecked with purple ; preserved specimens usually 

 yellowish-brown. Reaches a size of ca. 125 mm. diameter of 

 test. 



In British seas this easily recognisable species is very 

 common off the west coast of Ireland, in depths of ca. 600- 

 1800 m. ; also in the warm area of the Faroe Channel. It is 

 distributed from south of Iceland to the Gulf of Guinea, and 

 also from the Davis Strait to the West Indies. Bathymetrical 

 distribution ca. 275-2500 m. 



