43 
with the beginning development of a distinct suranal plate in 
Palæopedina, indicates that the ,,suranal" plate may have been 
acquired separately by different forms of Echinoids. In the light 
of this supposition it will be especially interesting to study the 
suranal plate of the Echinina. 
The existence of a suranal plate in this great division of the 
Echinoids was first pointed out by A. Agassiz”), later on by 
Lovén (Études, p. 74—75. Pl. XXI) for Strongylocentrotus drø- 
bachiensis. It has played an important part in the question about 
the homologies of the apical system, Lovén finding in this fact 
aåa direct proof of the correctness of his view of the homology 
between the Crinoid calyx and the Echinoid apical system. The 
a c 
Fig. 7. a. Calyx of Marsupites, b. ”hottal system of Salenia, c. Apical 
system of a young Strongylocentrotus drøbachiensis. (Slightly altered, 
from Lovén). 
three figures (Fig. 7) here copied from Pl. XXI, of Lovén's 
»Études", representing the calyx of Marsupites, the apical system 
of Salenia and of the young Strongylocentrotus make this easily 
understood; even the peculiar striping of the plates (omitted in 
the figure) is the same in all of them. 
The existence of this plate in general in the Echinina may 
be regarded as an established fact, even if only few species have 
been described or figured in quite young stages as e.g. Parechinus 
microtuberculatus by Bury in his ,,Studies on the Embryology of 
Echinoderms"”), or Sterechinus Neumayeri in the author's work 
»Die Echinoiden der Deutschen Sidpolar-Expedition", Taf. XVII. 
1) On the Embryology of Echinoderms. Mem. Amer. Acad. IX. 1864, p. 12. 
2) Quarterly Journ. Mier. Sci.” N. S. 39. 1889. Pl. XXXVIII. Fig. 12. 
