158 



ECHINOIDEA. I. 



sexually ripe individuals later grow to become large Kch. acutus of one or another form. Upon the 

 whole we know next to nothing of the biology of these animals. 



Echituis tiiicrostoiiui Wyv. Thomson (395. p. 744), of which Prof. Bell has sent me a couple of 

 specimens, is only b)- its uncommonly small peristome distinguished from Ech. acutus var. norvrgiciis, 

 in all the other respects it agrees completely with this latter. As there is, however, great variation 

 with regard to the size of the peristome in iiorvcgicus^ I can in Ecli. »iicrostonia see nothing but a 

 good >iorvegict(s. The strong red colour and the thinness of the test, pointed out by Wy v. Thomson 

 and Bell (Catalogue p. 149) as characters of Ecli. iiiicrostonia, are as well found in typical iiorvrgicus. 



Whether FaIi. nirln can be kept up as a distinct species, I do not \entiTre to say with certainty, 

 as I have onlv had a slight material of it for examination; but I am inclined also to regard this form 

 as a mere variety of Ech. acutus. Large specimens, to be sure, are very characteristic; but this holds 

 also good with regard to Ech. acutus var. mediterranean and I think it to be \'ery doubtful, whether 

 the smaller specimens may be distinguished with certainty. Koehler (221) has exactly enumerated 

 the characters by which Ech. acutus and iiielo are distinguished. The most important one is the fact 

 that in >i/clo only every other interambulacral plate above the ambitus has a primar\- tubercle, while 

 in acutus they ha\e all such a tubercle — with the exception of th( part near the apical area, where 

 it is also wanting on every other plate; in some specimens the latter arrangement ma\' even reach 

 down almost to the ambitus. Thus this character is rather unreliable. Koehler finds another char- 

 acter of importance in the tridentate pedicellaria;, the edge of which is in inrlo highly serrate, in acutus 

 almost smooth. According to my examinations, however, this feature is not at all constant; they ma>' 

 be thorny also in acutus and smooth in inelo. (The thorns* are in realit}' transverse series of small 

 teeth, as usual in the i?c/;/;/?/j-species). The other characters pointed out by Koehler, seem to me to 

 be of slight importance. I may further mention that the globiferous pedicellarice (PI. XVIII. Fig. 18) 

 are most frequently distinguished by the apophysis being peculiarly rugged or spinous above, and that 

 the spicules are somewhat larger than usual (PL X\TII. Fig. 8). As in acutus a primary tubercle is 

 only found on every other ambulacral plate, in several j^laces even on ever\- third plate only, and as 

 in Ech. acutus var. mcditcrrai/ca the pores are rather much remo\'ed from the edge of the ambulacral 

 area. — Thus I can see no one character b>- which Ech. mclo is decidedly distinguished from acutus, 

 and accordingly it can scarce!}- be maintained as a distinct species, but only as a variety of acutus.^ 

 characterized by its almost globular form, its green spines, and the ])eculiar coloration of the test. 



Of Ech. acutus we have a rather great number of specimens, all of vai\ iiorvegicus, or at all 

 events more nearly belonging to this variety, from the following stations (on the southern and western 

 side of Iceland, the Denmark Strait): 



St. 8 (63° 56' N. L. 24° 40' W. L. 136 fms. Bottom temp. 6° 4). i specimen. 



— 9(64=18' — 27° 00' - 295 — — 6°2). 2 — 



— 16 (65° 28' ^ 27° 05' -250- - 6° 4). I - 



— 52 (63° 57' — 13° 32' — 420 - — f 2). 2 — 



— 54 (63° 08' - 15° 40' - 691 — — 4° 2). 23 - 



— 85 (63° 22' — 25° 21' — 170 — — ? ). I — 



— 87 (65° 02' — 23° 58' — no — — ? )■ I — 



— 98(6537' ■ 26^27' -138- - 6=2). I 



