34 
acts known from the development of Austrocidaris and Rhyncho- 
cidaris, I have reexamined the question, the more so as I had 
scarcely fully realised the morphological importance of this state- 
ment, when that work was written, being at that time still not in 
doubt of the correctness of Lovén's view, that a central plate 
was typically present in the Cidarids. The reexamination of the 
specimen showed the above statement to be correct; there was really 
only one anal plate developed, occupying the whole — small — space 
between the five genital plates. In two other specimens of the 
same size, I find, however, in one three, in the other five or 
perhaps six anal plates developed; they were of somewhat diffe- 
rent size, which means that they are not developed quite contem- 
poraneously; but the difference is so gradual that there seems not 
the slightest reason to mark the first developed plate as a ,,cen- 
tral" or ,,suranal" plate. The plates were found covering one 
another with their edges so that it was only through dissociating the 
apical system (by Eau de Javelle) under the microscope that it 
became possible to determine the exact number of plates present. (One 
of the specimens examined was sent to me from the Berlin Mu- 
seum through Dr. R. Hartmeyer, for which I may here express 
my gratitude). 
A. Agassiz is inclined to lay some stress on the apparent 
fact that ,,the first formed anal plates occupy a radial position; 
that is, they occupy the same position which the so called infra- 
basals do in Ophiurans and Starfishes according to .Carpenter and 
Sladen”. — ,,These five radial plates always retain their prominence 
in the full grown Cidaris, and have as good a right to be consi- 
dered as infrabasals as the plates considered as such in the Ophiu- 
ridæ and Starfishes by Carpenter and Sladen" (Calamocrinus, p. 74, 
76). If this view were correct the early development of the anal 
plates should certainly be expected to show these five plates 
to begin nearly contemporaneously; this is, however, not the case. 
It has been shown that in the Cidarids thus far studied more 
elosely, the anal plates appear from the beginning in the number 
