ECHINOIDEA 299 



point slightly thorny, not thickened, bent somewhat inwards 

 (Fig. 148, 3) ; in the second stage it has epaulettes both at the base 

 of the postoral and postero-dorsal arms and at the posterior end 

 of the body (Fig. 147, 3). The young sea-urchin reaches in the 

 course of its first year a size of ca. 4 cm. in horizontal diameter, 

 and is then already sexually mature ; when 2 years old it is 

 4-7 cm., 3 years old 7-9 cm., 4 years old 9-11 cm.^ The^ery large 

 specimens of 15-16 cm. diameter are therefore probably 7-8 years 

 old. The food consists of both algae {e.g. Laminaria, especially when 

 covered with Bryozoa) and all sorts of minor animals, especially 

 barnacles. As food for man this species is much used in Portugal ; 

 according to Pennant it was also formerly thus used by the poor 

 in many parts of England. As parasites are found in this species 

 the Nematodes Oncholaimus echini Leydig and IcJithyonema Grayi 

 Gemmill and Linstow, and the Planarian Syndesmis echinorum 

 Shipley. Among its spines is not rarely found a polychsete worm, 

 Flabelligera affinis M. Sars. 



In British seas this species is common all round the coasts, 

 from the littoral zone (where it is, especially in the breeding 

 season, found among the algse on the rocks) down to ca. 40 m., 

 becoming much rarer beyond that depth and only exceptionally 

 found in greater depths than ca. 100 m. It is recorded from the 

 Lousy Bank. It is elsewhere distributed from Finmark and 

 Iceland to the coasts of Portugal, but is not known from the 

 Mediterranean. Various statements of its occurrence outside the 

 European seas are erroneous, resting on unreliable labelling. 

 Bathymetrical distribution, 0-ca. 1200 m. 



2. Echinus tenuispinus Norman. (Fig. 169.) 



(Syn. Echinus esculentus, Var. tenuispinus Norman.) 



Test globular, on the upper side rather bare, the secondary 

 tubercles being few and scarce, smaller than the primary tubercles, 

 which form fairly distinct longitudinal series. Spines short and 

 slender. On the oral side the spines and tubercles are more 

 numerous and larger. Only every second ambulacral plate has 

 a primary tubercle, the other plates, especially at the ambitus, 

 usually having a larger secondary tubercle in the median part 

 and another a little outside the primary series, near the pores ; 

 on those nearer the apical system the inner tubercle is more often 

 wanting. Small spines on the buccal plates. Pedicellariae as in 



^ According to observations by Elmhirst. 



