l6o ECHINOIDEA. I. 



1 6. Echinus esculentus L. 



PI. I. Fig. 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 spliæra O. F. Muller. 



— Sch'dHirtzii Nilsson & Holst. 



Principal literature: Sv. Nilsson & A. L. Holst: Collectanea Zoologiæ scandinavicæ. Lund. 

 1817. p. 7. — Diiben & Koren: Ofvers. af Skandinaviens Echinodermer. p. 264. — Sars: Norges 

 Echinodermer. p. 93. — Agassiz: Revision of Echini. p. 491. — Loven: Echinoidea descr. by Linnæus 

 (252). p.6i. — Hoyle: Rev. List of Brit. Echinoidea (202) p. 411. — Bell: Catalogue of Brit. Echino- 

 denn.s. p. 152. 



With regard to the other s}-non\ins and the other literature I shall refer to Rev. of Ech. 

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

 easily recognizable species, but only niention a few features which have hitherto beeu overlooked or 

 not clearly described. 



The primary tubercles are ver}- 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 hånd, the primary tubercles form very conspicuous longitudinal series, both in the ambir- 

 lacral and the interambulacral areas (PL I. Fig. 9), secondary tubercles being almost not \'et found liere. 

 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 011 every other ambulacral jDlate, below (and in young speci- 

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

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

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

 placed rather irregnlarly, 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 piates are found 110 secondary tubercles at all. — According to 

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

 tuberclesv. That an absorption of tubercles (and spines) once formed, ma\' take place, I must doubt; 

 it is, at all events, not the reason why primary tubercles are liere wanting on ever}- other (or still 

 more) ambulacral piates, the faet being that the)' have never been formed on these piates. — 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 wliite colour. 



The close-set spines are short and thick, rarely longer than 14 — 15'"™; in small specimens the 

 spines are comparatively longer than in the large oiies, 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 frequenth' somewhat blunt, worn, I suppose, by 

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

 appearance, being finely, irregnlarly striped longitudinally 011 the ribs (PI. XX. Fig. 30); this holds 

 otherwise also good with regard to the other ijf/;/;/,'/j-species, as well as Strongylocoitrotus and 



