TH. MORTENSEN, 
H 
(Schwed. Südpolar-Exp. 
PENTEr): no detailed description or figures being given by ANDERSSON this could 
not be decided by Clark. As will be evident from the description given here the 
identity with Carpenter's Antedon angustipinna is out of question, alone the dif- 
ferences in the oral pinnules being so great as to decide the matter. It is much more 
the question whether the species described here can really be retained in the genus 
Isometra , one of the more important characters of the genus being that the oral pin- 
nules are slender, »styliform«, with elongate joints, which does not fit very well with 
the present species. Still, I prefer to leave it in the genus Isometra in spite of this 
and other minor discrepancies; the expanded joints of the genital pin- 
nules being the main character of the genus. It is true, this widening 
is much more developed than in the type species; but this would hardly 
be a good reason for excluding this species from the genus, as it is 
evidently a special adaptation for the care of the brood; and, in regard 
to this question, it is decidedly more important that the male genital 
pinnules are also expanded, and in a way corresponding very closely to 
what obtains in the type species (»Challenger« Comatulidæ, PI. XIII, 
Figs. 5 a, b). 
The main interest with this species, of course, attaches to its care 
of the brood and the special adaptations connected therewith. After 
the careful description given by K. A. ANDERSSON in the paper quoted 
there is no reason to enter here again in a more detailed way on this 
matter. I can in general confirm Andersson’s observations, as well 
with regard to the way the brood is cared for, as with regard to the 
tentacle of Iso- remarkable fact that the central cavity of the ovary contains numerous 
metra vivipara , S p erma t 0 zoa, which appear to enter through the wall of the ovary to- 
rn ventral aspect, 
showing the slit- wards the brooding chamber, not through a preformed opening. As 
like opening of K. A. ANDERSSON says, this would appear to necessitate a sort of copu- 
nmrsupmm. j a ^ Qn j n ^j g S p ec i es 'file fertilization probably occurs within the ovary 
itself. I have, however, not succeded in finding any fertilized eggs still 
lying within the ovary; on the other hand I have not observed any unfertilized eggs 
either within the brooding chamber. 
The shape of the brooding chamber may be seen from PI. II, Figs. 6 — 7 and 
textfig. 13. The ventral side of the marsupium is formed by a thin, naked membrane, 
with no calcareous deposits in it. The short, narrow, slitlike opening is situated close 
to the ambulacral furrow. 
A detailed account of the embryonal development will be given in the memoir 
under preparation, as mentioned in the introduction. I would here only state a few 
facts concerning the later larval stages. 
