158 



ECHINOIDEA. I. 



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

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



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

 specimens, is only by its uncommonly small peristome distinguished from Ech. acutus var. norvegicus, 

 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 norvegicus, I can in Ecli. microstoma see nothing but a 

 good norvegicus. The strong red colour and the thinness of the test, pointed out by Wyv. Thomson 

 and Bell (Catalogue p. 149) as characters of Ech. microstoma , are as well found in typical norvegicus. 



Whether Ech. melo can be kept up as a distinct species, I do not venture to say with certainty, 

 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 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 very doubtful, whether 

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

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

 that in melo 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 may even reach 

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

 acter of importance in the tridentate pedicellarise, the edge of which is in melo highly serrate, in acutus 

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

 be thorny also in acutus and smooth in melo. (The thorns are in reality transverse series of small 

 teeth, as usual in the isr/'///,7.v-speeies). The other characters pointed out by Koehler, seem to me to 

 be of slight importance. I may further mention that the globiferous pedicellariae (PL 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 (PI. XVIII. Fig. 8). As in acutus a primary tubercle is 

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

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

 area. - Thus I can see no one character by which Ech. melo is decidedly distinguished from acutus. 

 and accordingly it can scarcely be maintained as a distinct species, but only as a variety of acutus, 

 characterized by its almost globular form, its green spines, and the peculiar coloration of the test. 



Of Ech. acutus we have a rather great number of specimens, all of var. norvegicus, 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 c 40' W. L. 136 fans. Bottom temp. 6° 4). 



9 (64° 18' 27°oo' 295 - 



16 (65 28' 27 05' - 250 - 



- 52 (63° 57' i3° 32' — 420 - 



54 (6 3 °o8' 15° 40' 691 - 



■ 85 (63 J 22' 25°2l' IJO 



87 (65 : ' 02' - 23° 58' — no - 



- 98 (65 37' 26° 27' - 138 - 



