39 
of any Salenid. A. Agassiz („Blake u Echini, p. 18) gives some 
information of tke apical system in the young Salenia varispina 
of 1,6 mm diameter; it is stated to be at that size already 
essentially as in the grown specimens; „the suranal plate is at 
first quite small, a narrow plate on the side of the anal system 
opposite the nearest ocular plate. It appears to gain in size at 
the edges adjoining the genital plates u . The first appearance of 
the suranal plate has, however, not been observed, the specimen being 
probably too old already (—the figure, PI. VI, 1., does not give 
the apical system sufficiently detailed; the suranal plate is not to be 
distinguished in it —). The anal system is distinctly pentagonal 
and covered by eight large, triangular plates with rounded tips. 
In the young Salenia miliaris there are five 1 arger and some small 
plates along the edge of the anal area. Upon this evidence it 
seems somewhat rash to conclude that „it appears that the anal 
system of Salenia, as of Cidaris, was 
originally covered by five plates“ (A. 
Agassiz. Panamic Deep Sea Echini. 
p. 86). 
While thus the embryology does 
not as yet afford the knowledge wanted 
of the development of the remarkable 
suranal plate of the Salenids, palæ¬ 
ontolog} 7 seems to have shown us the 
way in which it has originated. In 
several species of the genus Acrosa- 
lenia, there is not one single large 
suranal plate, but several of diffe- 
rent size, so arranged as to diminish in size towards the peri- 
proct, as shown in the fig. 4, representing the apical system 
of a specimen of Acrosaienia angularis (Ag.) Desor x ). It is here 
scarcely possible to distinguish between the „suranal“ plate and 
Pig. 4. Apical system of Acro¬ 
saienia angularis (after D e 
Loriol). 
The genital pores are not indicated 
in the original figure. At the mark 
the figure has been slightly restored. 
9 From P. de Loriol. Premier Supplement å l’Échinologie helvétique. 
Mém. Soc. Pal. Suisse. XII. 1885.. PI. I. Fig. 4. 
