78 
TH. MORTENSEN, 
(Schwed. Südpolar-Exp. 
Fig. 9. AGASSIZ does not give a detailed explanation of this or the other figures, 
and I am unable to grasp his meaning fully from the numbers put on the plates. 
But there can be no doubt of what is considered the Ocular III, it must be that 
with the tentacle; inside this plate are seen 3 smaller plates, two outer paired, and 
one inner single. What are these plates? In the figure 307 they are seen to be 
provided with pores; in the figure 308 these pores have metamorphosed into tu- 
bercles, but judging from PI. 99. Fig. 7 they would much sooner represent tubefeet. 
This would mean that they represent the Ocular III and two ambulacrals, and the 
comparison with the figure 16 leaves no doubt that this is the true explanation. 
The alleged ocular plate outside must be incorrectly drawn, and likewise the odd 
tentacle has got a wrong place. When this has been made clear the identification of 
the rest of the plates is easy enough; it will be sufficient ro refer to the two figures. 
Regarding the actinal side of the test in the figures quoted of the »Panamic Deep 
Sea Echini» I would only remark that Professor Agassiz’ surprising statement of 
the sternum forming »almost a true meridosternum» (p. 212) is evidently due to a 
misconception. It is, as should be expected, a true amphisternum, the two sternal 
plates being quite equally developed in the anterior end; the fact that one is slightly 
longer than the other at the aboral end, a character well known in different types 
of amphisternum, especially the more primitive, is likewise only what should be 
expected. (Cf. »Ingolf» Echinoidea. II. p. 84.) 
The next stage observed is that of the fully developed young, ready to leave 
the marsupium, 2.5 mm. in length * (Figs. 17 — 18). The most important change to 
* In a fragment of a large specimen, probably of Abatas cavernosus , from the Magellan Strait (the 
Hamburg Museum) I find the young ones in the marsupium considerably larger, 3.5 mm. in length. The 
transverse band of the fasciole has not yet appeared in these specimens. 
