Bd. VI: 8) 
THE CRINOIDEA. 
17 
The generic position of this curious little Crinoid is somewhat difficult to decide, 
especially on account of the absence of fully developed cirri, the important characters 
derived from their structure remaining unknown. The characters of the centrodorsal 
point towards the subfamily Ba thymetrin æ , and also the two first pinnules are in 
accordance with the characters of this subfamily. I think then that it must belong 
here, representing a new species of the genus Thaumatometra. 
The main point of interest with this species is its viviparity, the more so on ac- 
count of the peculiar way in which the brood is cared for, a way entirely different 
from that which is used by the two other viviparous species. 
The eggs, when ripe, must find their way through the wall of the ovary into the 
marsupium, which is a pocket-like groove on the side of genital pinnule (PI. V, Figs. 
2, 5); it is found now on the proximal, now on the distal side of the pinnule. The 
section of a genital pinnule (one of the oral pinnules, with no ambulacral furrow) 
represented in PI. V, Fig. 7, shows the still empty marsupium as a deep, narrow side 
fold, the opening being a quite narrow slit. On the pinnules with large Pentacrinoids 
the marsupium is widely opened, as seen in PI. V, Fig. 5. The fertilization must 
take place in the marsupium; spermatozoa are not found within the ovary, as is the 
case in Isometra vivipara. The eggs are small, ca. 0,15 mm. No developing eggs 
were found in the marsupium in any of the pinnules preserved, so that no informa- 
tion can be given of the embryonal development. 
The larvæ do not leave the marsupium, when ready to metamorphose in to Penta- 
crinoids; they remain in the marsupium, attaching themselves with their 
stalk (most probably by means of the sucking disk) to the wall of the marsu- 
pium, only with the head and upper part of the stalk protruding through the opening. 
In this place they remain throughout their whole development, until they 
are ready to detach themselves from the stalk. PI. V, Figs. 3 — 6 represent 
different stages of Pentacrinoids attached to the parent pinnule. The point of fixation 
varies; in P'ig. 3 it is near the opening, in P'ig. 4 it is at the very bottom of the 
marsupium. In the elder stages I have constantly found the stalk attached to the 
second or third pinnule joint, which has a lateral widening corresponding to the base 
of the Pentacrinoid stalk. In one case the stalk is attached to the articular surface 
between the third and fourth pinnule joints, which are both widened. No terminal 
stem plate is found. „ 
The young Pentacrinoid is very small, but in the course of its development it 
grows to a very considerable size (PI. V, Fig. 6). These large Pentacrinoids attached 
to the pinnulae of the tiny mother specimen gives this species a very curious ap- 
pearance. Sometimes two Pentacrinoids are attached to the same pinnula (PI. V, 
Fig. 5); they are in about the same stage of development in the case figured, but in 
3 — 173534. Schwedische Südpolar- Expedition iqoi — 1Q03. 
