32 
papillata of 2,4 mm diameter. Though the limits of the plates on 
the anal area are not distinctly shown in the figure, it is certain 
that there is no trace of a primordial central plate, and Agassiz 
so far rightly states (Calamocrinus, p. 74) that „there is nothing 
known to prove that in the Cidaridæ the anal system is not in the 
earliest stages covered by five plates, as in the Arbaciadae it is 
covered by four“. 
The above quoted descriptions of the anal system of young 
Cidarids do not prove anything definite as to the question whether 
there is originally a single large suranal plate or not, the spe- 
cimens being already too old. It is through the embryos of 
Austrocidaris canaliculata , Rhynchocidaris triplopora and Noto- 
cidaris gaussensis that we have gained definite knowledge thereof, 
all these species having care of the brood, so that stages young 
enough to show the first formation of the anal plates have been 
comparatively easily obtainable. 
A pair of young specimens of Austrocidaris canaliculata are 
figured on PI. II. figs. 8—10 of the „Challenger“ Echinoidea, 
without showing, however, any details of the apical system. A more 
detailed study of the development of the test of this species was 
first given by Lovén, in his „Echinologica“ x ), the result of his 
researches being, as regards the anal system, that „in the centre 
there is a small, clear, irregularly pentagonal space, covered by 
the general integument (PI. II. fig. 3). In another specimen (PI. II. 
fig. 5) this space has just been filled with the dorso-central disk 
(PI. II. fig. 6), a still delicate pentagonal lamina of reticulated 
calcified tissue, with its thin margins now overlying, now under- 
lying those of the costals, in its middle thickened and raised into 
the beginning of a verruca“. (Op. cit. p. 5—6). 
Here then it seems that the presence of a suranal (central) 
plate in the Cidarids has been definitely proved; especially the 
quoted fig. 6 of Loven’s paper seems convincing. Nevertheless 
0 Bill. Sv. Vet. Akad. Handl. 18. 1892. 
