38 
of Lovén (Études p. 75) that ,,dans les Échinocidaris, il parait 
que Vouverture anale se pratique an moyen d'un soulévement cen- 
tral, par suite duquel le disque, détaché tout autour, se fend en 
quatre lames triangulaires". But it is very desirable that the first 
formation of these plates should be really observed. 
Regarding the position of the anal plates it is noticeable that 
in those forms which have normally five anal plates they are 
placed radially in one form (Habrocidaris), interradially in another 
(Pygmæocidaris). It is then evident that we find here no support for 
the suggestion that there were originally five radially placed anal 
plates, and there is no reason to suppose that ,,the Arbaciadæ 
with only four anal plates we may consider as having one of the 
five radial plates atrophied" (Calamocrinus p. 78). 
The periproct of the Cyphosomina is very similar to that 
of the Echinina, the anal opening lying excentric. Whether aå sur- 
anal plate is typically present or not cannot be decided from the 
evidence at hand; the question can scarcely be settled before the 
development of the recent form, Glyptocidaris crenularis A. ÅAg., 
has been studied. 
The Salenidæ show the central or suranal plate in its full 
development (Fig. 7, b. p. 43); they afford the main foundation 
for the homologizing of the Echinoid apical system and the Crinoid 
calyx, and have, indeed, given rise to the ,,Crinoid""-theory through the 
special development of the suranal plate, ,,die verfibrerische Sub- 
analplatte", as the Sarasins designate it. AA most important 
feature of this plate is its position outside the anal area. 
The embryonal or post-embryonal development is not known 
XIII. No. 337. 1901, p. 938), besides specimens with five or three 
anal plates instead of the normal four, a specimen (fig. 21) in which 
one of the four anal plates (the left anterior) has increased to a large 
size, so as to occupy nearly the whole anal area, the other three 
remaining quite small. The large plate quite resembles a suranal 
plate and may thus far well be regarded as such. But this abnormal 
case can certainly not afford the proof that a suranal plate is nor- 
mally present in the Arbaciids, all other evidences tending to show 
the opposite. 
