T 6o ECHINOIDEA. I. 



1 6. Echinus esculentus L. 



PI. I. Kg. 9. PI. III. Fig. 3. PI. XV. Figs, i, 5. PI. XVI. Figs. 7, 12. PI. XVIII. Figs. 12, 13, 20. PI. XIX. Figs. 24, 28, 30. 



PI. XX. Figs. 24, 30. 



Principal synonyms: Echinus sphcera O. F. Mullet. 



Schwartzii Nilsson & Hoist. 



Principal literature: Sv. Nilsson & A. L. Hoist: Collectanea Zoologiae scandinavicse. Lund. 

 1817. p. 7. -- Diiben & Koren: Ofvers. af Skandinaviens Echinodenner. p. 264. - - Sars: Norges 

 Echinodermer. p. 93. Agassiz: Revision of Echini, p. 491. Loven: Echinoidea descr. by Linnaeus 

 (252). p. 61. -- Hoyle: Rev. List of Brit. Echinoidea (202) p. 411. -- Bell: Catalogue of Brit. Echino- 

 derms. p. 152. 



With regard to the other synonyms and the other literature I shall refer to Rev. of Ech. 

 and Bell's Catalogue. -- I shall not here give any thorough description of this well known and 

 easily recognizable species, but only mention a few features which have hitherto been overlooked or 

 not clearly described. 



The primary tubercles are very small, both in the ambulacral and the interambulacral areas, 

 so that they are only by a closer inspection seen also in this species to form regular longitudinal 

 series in the interambulacral areas, even in the largest specimens (PI. XV. Fig. 5). In small specimens, 

 on the other hand, the primary tubercles form very conspicuous longitudinal series, both in the ambu- 

 lacral and the interambulacral areas (PL I. Fig. 9), secondary tubercles being almost not yet found here. 

 The series of primary tubercles in the ambulacral areas is in large specimens very indistinct (PI. XV. 

 Fig. i); a primary tubercle is only found on every other ambulacral plate, below (and in young speci- 

 mens) the alternation of the tubercles, however, is most frequently very irregular, and above the 

 ambitus also 2 3 plates without primary tubercle may follow each other, sometimes also a couple 

 of plates with primary tubercle. The secondary tubercles on the plates wanting primary tubercle are 

 placed rather irregularly, the most common arrangement, however, being that a larger tubercle is 

 found near the median edge of the plate, and a small one outside of the primary series, quite at the 

 pores. On the uppermost ambulacral plates are found no secondary tubercles at all. >- According to 

 Bell (Catalogue, p. 153) the irregularity may be further increased by absorption of some of the 

 tubercles. That an absorption of tubercles (and spines) once formed, may take place, I must doubt; 

 it is, at all events, not the reason why primary tubercles are here wanting on every other (or still 

 more) ambulacral plates, the fact being that they have never been formed on these plates. - - The 

 miliary tubercles are very little conspicuous, being of the same deep red colour as the test, while 

 the other tubercles just are so conspicuous on account of their white colour. 



The close-set spines are short and thick, rarely longer than 14 i5' nm ; in small specimens the 

 spines are comparatively longer than in the large ones, scarcely, however, in any instance more than 

 half the length of the diameter of the test. The spines on the actinal side are generally somewhat 

 flat, but not widened at the point; the end is most frequently somewhat blunt, worn, I suppose, by 

 the walk. Under higher magnifying powers the surface of the spines is seen to have a peculiar 

 appearance, being finely, irregularly striped longitudinally on the ribs (PL XX. Fig. 30); this holds 

 otherwise also good with regard to the other Ec/iinus-species, as well as Strongyloccntrotus and 



