262 



AMONG THE SEA URCHINS. 



indented, is not at all like the woodcut in Taylor's "Half-hours 

 at the Seashore," which is the only drawing we have ever seen 

 of it. The indentations, in fact, are points of continuous 

 growth, always irregular. The muscular coating of the sucker 

 covers the plates, entering the perforations and binding the whole 

 together ; while immediately under the terminal disc plates lie an 

 equal number of oblong plates, forming a circlet or calcareous ring 

 (PL XVIlI.,Figs. 2 and 3). Fig. 4, PI. XVIIL, is an enlarged draw- 

 ing, showing how they fit on to each other. The muscular flesh, 

 penetrating the pores, holds them in situ. This circlet, though, we 

 believe, it was never before drawn, is called by Luven the ''''foot-ring^^ 

 " aiinulus^^ or '■'' psellion^'^ and forms the passage up the tube, the 

 spicules referred to on p. 17 supporting the muscular flesh above. 



But we must now introduce our 

 readers to the masticatory apparatus 

 of the "Regular" P^chini, as those 

 Sea Urchins are called whose 

 rounded tests possess on the under 

 side those powerful teeth which 

 enable some of their possessors to 

 carve out for themselves round 

 holes or depressions even in the 

 granite rock where they are safe 

 from the fury of the Atlantic gales, as we found them in the north 

 of Ireland last summer. In the above illustration, Fig. 3, the tips 

 of the teeth are seen projecting from the shell of the Purple Sea 



Fig. 3. — Buccal armature of 

 Strongyloce7itroius lividus. 



Fig. 4. — Interior of Test, with Dental Pyramid of Purple Sea Urchin. 



