146 



ECHINOIDEA. I. 



13. Echinus Alexandri Dan. Kor. 



PI. V. Figs. 2— 3, 5—7. PI. XV. Figs. 13, 17. PI. XVI. Fig. 8. PI. XVIII. Figs. 9, 11, 19, 23, 25. PI. XIX. Figs. 1 5, 31, 34, 38. 



PI. XX. Figs. I, 2, 27. PI. XXI. Figs. 18—20, 27. 



Literature: Danielssen & Koren (109). — Danielssen (no): Echinida. Norske Nordhavs- 

 exped. p. I. T.I. — Koehler (224—226): Echinodermes. «Caudan . p. 92. PI. I. fig. 4 PI. II. fig. 18— 19. 



Of this large, fine species we have a very great material from the ringolf ., and as I have had 

 the type specimen of Danielssen for examination, I have been able to identify it with certainty. 

 Prof. Koehler has further sent me some of his specimens from tCaudan , so that I am also able to 

 corroborate the correctness of his determination. On the basis of this great material I shall then give 

 a new description of the species. 



The test is much flattened, the height generally a little less than half the diameter of the test; 

 specimens of a middle size and smaller ones are quite flat above, the larger ones a little rounded. The 

 actinal side is flat, not at all or very little curved inward at the edge of the mouth. The slits as 

 usual small and rather indistinct. 



All the measures in millimetres. 



The ambulacral areas (PI. XV. P^ig. 13) in large specimens scarcely half as broad as the inter- 

 ambulacral areas, in smaller specimens a little more than half this breadth; at the edge of the mouth 

 the two areas are of about equal breadth. The number of compound plates in the ambulacral areas 

 is only about V2— V3 time greater than that of the interambulacral areas, accordingly the ambulacral 

 plates are rather high. The arcs of pores are not placed verj- obliquely, in small specimens the)- are 

 almost perpendicular. In the type specimen the arcs of pores show a remarkable irregularity, as is 

 seen in the figures of Danielssen. As no similar feature is seen in any of the Ingolf-specimens it is 

 no doubt something abnormal. The pores reach quite to the edge of the ])late.s. The boundaries 

 between the small plates rather indistinct, the boundar\- line between the areas rather highly sinuate. 

 The primary tubercles form a ver\- conspicuous, dense longitudinal series; a primary tvibercle is found 



