418 



ECHINODP]RMS OF THE BRITISH ISLES 



mid-radius, excepting a few at each end ; rarely a few are found 

 scattered in the mid-hne, very rarely a double row may be found 

 along the mid-radius. Along the edges the tube-feet form a 



Fig. 253. — Psolus squamatus ; dorsal and ventral side. Nat. size. 



conspicuous double row. Scales large, smooth, with sparse small 

 grains on their surface. No small scales intermingled betw^een 

 the large ones on the mid-dorsal side, between mouth and anus. 



Fig. 254.- — Deposits from the ventral sole of Psolus squamatus (1) and Ps. 

 valvatus (2-3). 3. Half in side view in order to show the peculiar shape 

 of the tubercles. x 145. (From Danmark's Fauna.) 



The grains on the scales flattened, ca. 0-15-0-2 mm. in diameter. 

 The deposits of the ventral sole are small, delicate plates, smooth 

 or with very few small tubercles (Fig. 254, 1). No cup-shaped 

 bodies. All retractor muscles attached to the longitudinal 

 muscles. Colour whitish-yellowish. Grows to a length of 6-7 cm. 



