244 Th. Mortensen. 



til Myzostomernes Anatomi og Histologi. 1885. p. 7). On the evi- 

 dence of the present scarce material it is, of course, impossible to 

 decide, whether this small size is the normal for the form infesting 

 H. prolixa, or whether they are only young specimens. In case they 

 are really fullgroAvn, they will evidently form a separate species. 

 I notice as a difference from the typical form of M. Carpenteri, as 

 described and figured by Nansen (Op. cit., p. 7, PI. I., figs. 6 — 7), that 

 dorsal ridges are not distinct. For the rest the shape of the animal 

 is in rather close accordance with the figures given by Nansen, 

 whereas the figures given by v. Graff in his work on the "Chal- 

 lenger" Myzostomida (Scient. Res. of the Voyage of H. M. S. "Chal- 

 lenger", XXVII., 1884, PI. II., Figs. 10—15) are not so very similar. 



While thus the disk and the arms of H. prolixa are легу clean 

 and free from foreign organisms, the case is quite different with the 

 cirri. Quite a number of different animals may be found attached to 

 them. One of the commonest forms is Truncatulina lobatula Walker & 

 Jac, a Foraminifer characteristic through "the tendency displayed by 

 adherent specimens to form for themselves a covering of loosely agglu- 

 tinated sand" (Brady: "Challenger" Foraminifera, p. 660), a feature well 

 shown by the present specimens. P. H. Carpenter has already 

 recorded this species from the cirri of arctic Comatulids, without 

 naming the species, on which it was found. (Stalked Crinoids. "Chal- 

 lenger", p. 134). Further, several small Hydroids of the species La- 

 foea fruticosa{Sars), Calyçella syringaL., Cuspidella sp. and Stegopoma 

 fastigiatum Alder'; a serpulid, egg capsules, young colonies of the 

 Bryozoan Gemellaria loricata and finally an entoprocte Bryozoan, 

 Loxosoma, probably representing a new species, which I hope to 

 have occasion to describe later on. 



Considerably more* important and interesting is, however, the 

 fact that on the cirri of this species are found Pentacrinoid- 

 larvæ, which are evidently its own brood, as might be concluded 

 alone from the fact that this species was quite dominating on the 

 locality (Stat. 99), only a single specimen of Heliometra glacialis being 

 found together with the numerous specimens of H. prolixa. Further- 

 more the Pentacrinoid oî H. glacialis (described by Levinsen, Kara- 

 havets Echinodermata, p. 414—15, Tab. XXXV., Fig. 8) differs con- 

 siderably from it in several features. It may thus be regarded as 

 an established fact that it is the larva of Hathrometra prolixa. A 

 good series of developmental stages is represented. They are in 

 several regards of considerable interest, and it has thus been thought 

 desirable to give a full account of the different stages, the more so as the 

 postembryonal development of Crinoid larvæ has been studied more clo- 



' 1 am indebted to Mr. P. Kramp for the identification of tliese H^'droids. 



