15« 



ECHINOIDEA. I. 



sexualh- ripe individuals later grow to become large Ecli. acutus of oiie or another form. Upon the 

 whole we know next to iiothing of the biology of these animals. 



Echinus microstoma Wyv. Thomson (395. p. 744), of which Prof. Bell has sent me a conple of 

 speciniens, is only b\- its uncommonly small peristome distinguished from Eclu actitiis var. norvcgiats, 

 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 i/orvegictis, I can in «.Ech. Diicrostonia« see nothing but a 

 good nor7iegicns. The strong red colonr and the thinness of the test, pointed ont b\- Wyv. Thomson 

 and Bell (Catalogne p. 149) as characters of Ech. iiiicros-foiiia, are as well fonnd in typical i/orvrginis. 



Whether Ech. indo can be kept np as a distinct species, I do not \enture to say with certaint\, 

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

 as a mere variety of Ec/i. aciitus. Large specimens, to be sure, are very characteristic; but this holds 

 also ofood with regard to Ech. aaifits var. iiicditcrraiica^ and I think it to be ver\" doubtfnl, whether 

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

 the characters by which Ech. acutus and inrlo are distinguished. The most important one is the faet 

 that in indo only every other interambulacral plate above the ambitus has a primary tubercle, while 

 in acutus they have all such a tubercle — with the exception of the part near the apical area, where 

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

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

 acter of importance in the tridentate pedicellariæ, the edge of which is in indo highly serrate, in acutus 

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

 be thoru\- also in acutus and smooth in indo. (The thorns are in realit\- transverse series of small 

 teeth, as usual in the isr/z/V/^j-species). The other characters pointed out by Koehler, seem to me to 

 be of slight importance. I may further mention that the globiferous pedicellariæ (PI. X\TII. Fig. 18) 

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

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

 only found on every other ambulacral plate, in several piaces even on every third plate only, and as 

 in Ech. acutus var. incditcrranca the pores are rather much removed from the edge of the ambulacral 

 area. — Thus I can see no one character by which Edi. indo is decidedly distinguished from acutus, 

 and accordingh' it can scarcely be maintained as a distinct species, but only as a variet}' of acutus, 

 characterized b\- its almost globular form, its green spines, and the peculiar coloratiou of the test. 



Of Ech. acutus we have a rather great number of specimens, all of var. norvcgicus, 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): 



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



