KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 39. N:o |. 91 
Furthermore, they also figure the nervous cord in a situation, that is by no means 
consistent with its actual position. It is true enough that, in forms with only two 
retractor-muscles, the nerve passes backward between those muscles, but it ought to 
be remembered that then the two muscles are ventral, quite similar and of the same 
size, and attached exactly at the same height in the animal. In the present case, 
on the contrary, when the retractors are of unequal size and attached with their 
bases at different heights, the one must be dorsal and the other one (or two, accor- 
ding to my view) ventral. In this case the nervous cord always runs towards the 
split between the bases of two united ventral retractors. 
Thanks to the kindness of Dr APPELLÖF of Bergen, I have had the opportunity 
of examining the very dilapidated remains of the original specimen of KOREN and 
DANIELSSEN, and I believe that my view concerning it is in conformity with the 
truth. Consequently, my own experiences are quite contrary to those of SELENKA 
(DE MAN & Börow), who say: "Wir reproduciren daher in kurzen die vortreffliche 
Beschreibung von KOREN and DANIELSSEN'". 
With a reference to my first paper of 1875 and to Figs. 96—108 and 210 in 
this report, the following characters may serve to distinguish Phascolion tuberculosum 
from Phascolion strombi. 
1:o) The tentaeceles are obtuse and, as it seems to me, limited in number to 
16, though, of course, this number may be smaller according to the age of the 
animal. 
2:0) The hooks behind the tentacles have a quite different appearance in the 
two species (Cp. the Figs.). 
3:0) The body is devoid of all traces of the characteristic girdle of darkish colou- 
red horseshoe-shaped bodies, familiar in other forms of the genus Phascolion. 
4:0) The retractor-muscles are attached somewhat in front of the posterior ex- 
tremity of the body and do not differ noticeably in size. 
Aspidosiphon mirabilis THEEL 1875. 
Pl. VIII. Figs. 111—119. 
Habitat: 
West Coast of Sweden, Bohuslän, 1 sp. West Coast of Norway, S. of Bergen 
or the ”reef of Jutland' (the Shetland Islands), 100—170 fms, 1 sp. — Trondhjem 
Fjord, Rödberg, mud, 200 m., 1 sp. (Mus. U-). 
With a reference to my former paper of 1875, I adduce the following state- 
ments as a supplement to it. Having had only two specimens available for investi- 
gation, the condition of which leaves a great deal to be desired, what I am here 
able to add is of but little significance. When I described this species in 1875, I 
had had only one specimen to examine, and now, after nearly 30 years, I have only 
one more at my disposal. Besides, the locality "S. of Bergen” is dubious, because 
