45 
appears mucli later than the genital and ocular plates, in accor- 
dance with what has been found in the other Echinoids thus far 
examined. — In the „Ingolf u -Ecliinoidea I, p. 89, PI. VII. Figs. 
6—8. II, p. 172, I have given some information on the devel- 
opment of the skeletal plates in Hypsiechinus coronatus Mrtsn. 
Concerning the suranal plate it is stated that in the more advanced 
stages „only one large anal plate is found (PI. VIL Fig. 14), which 
may be perforated by a larger opening; accordingly it seems quite to 
encompass the anal aperture“. This statement is incorrect. I have 
reexamined my preparations and find that in the stage represented in 
PI. VIL Fig. 6 the central plate has 
not yet appeared. In the stage 
represented by PI. VII. Fig. 8 
the central plate has made its 
appearance as a small plate 
occupying the middle of the 
space enclosed by the large ge¬ 
nital plates. (Fig. 8). There is 
no larger hole in the central plate, 
which might be supposed to re¬ 
present the future place of the 
anal opening. The plate figured 
in PI. VII, fig. 15 of the work 
quoted is evidently the madreporic 
plate; the misconception is due to the faet that the specimen from 
which it has been figured has been placed in an oblique position, 
so that this plate apparently occupied the centre of the apical 
system. 
The Echinina do not lend any support for the suggestion of 
Agassiz, that there were originally five radially placed anal 
plates. It is true that Pleurechinus hotliryoides has five larger 
radial anal plates among a larger number of smaller ones; but 
this single case, evidently, cannot be of mueh value against the 
evidence afforded by all the rest of this numerous group — especially 
Fig. 8. ' Apical system of a young 
Hypsiechinus coronatus. 
The five large plates represent the genital 
plates; the ocular plates have been omitted, 
being not in contact as yet with the ge¬ 
nital plates. 110 /i. 
