416 ECHINODERMS OF THE BRITISH ISLES 



intcrradii.i Deposits of the ventral sole of two sorts : small 

 cups and larger, spherical or oval bodies, of a rather com- 

 plicate structure (Fig. 252). Grains on the scales globular, 

 ca. 0-3 mm. in diameter. Colour yellowish-brown, larger speci- 

 mens often nearly black. Tentacles orange. Grows to a length 

 of ca. 15 cm. 



Young specimens differ, according to size, more or less con- 

 spicuously from the adult in their general appearance. They 

 may be very flattened, and the "tail", which is not yet very 



Fig. 251. — Psolus phantapus ; in side view. The tentacles and the fore-end 

 retracted. On the under side the ventral sole is seen. Nat. size. 

 (From DanmarFs Fauna.) 



conspicuous, may be quite retracted. The ventral sole is rela- 

 tively much broader than in the adult, and the tube-feet of the 

 mid-radius not yet developed. Such specimens, in fact, look 

 very much like Ps. squamatus. They may, however, be dis- 

 tinguished with full certainty from the latter species by the 

 deposits of the ventral sole, and by the character of the 

 dorsal retractor muscles, as stated above. Also the scales of the 

 dorsal side are already in specimens of 5-10 mm. length distinctly, 



^ This character of the retractor muscles affords a very reliable distinc 

 tion between this species and Ps. squamatus in the young stages, where 

 they are rather alike. 



