44 
Fig. 27). Generally tbe grown specimens retain distinet traces of 
the primordial large suranal plate, and sometiraes it is retained 
also in the grown specimens as a very large plate, covering nearly 
the whole anal area, as e. g. in Genocidaris maculata A. Ag., 
Pieurechinus Scillæ (Mazzetti); in the latter species some speci¬ 
mens even have, upon the whole, no other anal plates developed 
besides the suranal plate x ). In remarkable contradistinction to 
this species an other species of the same genus, Pieur echinus Doder- 
leini Mrtsn., has the whole anal area covered by numerous small 
plates, among which no trace of a suranal plate can be detected 2 ). 
A very similar case is afforded by Prionechinus Chuni Doderlein; 
however, Doderlein thinks he can distinguish a slightly larger 
plate near the edge of the anal area, which may represent the 
suranal plate 3 ). In any case it would be very interesting to 
examine quite youug stages of these species in order to state, 
whether a suranal plate is originally present here or not. The 
same would apply to Parasalenia with its peculiar four anal plates, 
recalling the condition in Arbacia. 
Some observations on the development of the apical plates in 
the young embryo of Parechinus microtuberculatus are given by 
Bury in his papers „Studies in the Embryology of Echinoderms“ 
and „Tire Metamorphosis of Eehinoderms“ 4 ), Though the first 
appearance of the suranal plate is not shown, still the important 
faet is to be derived from his observations that the suranal plate 
q It no longer holds good then that „there is no Echinoid known 
.... in which in the adult a single plate covers the anal system“, 
as is maintained by Agassiz against the S ar as i ns (Calamocrinus, 
p. 79, Note). 
2 ) Th. Mortensen. Siam-Echinoidea I. Tab. II. Fig. 1. 
3 ) Die Echinoiden d. deutschen Tiefsee-Expedition, p. 192. Taf. XXIV. 
Fig. 3. 
4 ) Quarterly Journ. Mier. Sc. N. S. Vol. 29. 1889, p. 33—35. PI. 38. 
Figs. 10-12. Vol. 38. 1895, p. 78—80. PI. 7. Fig. 34. PI. 8, figs. 36- 
38. The observations of Joh. Muller and A. Agassiz are not 
sufficiently detailed for the present purpose as regards the development 
of the apical system. 
