lUHANG TILL K. SV. VET.-AKAl). HANDL. BAND 18. AFI). IV. N:0 1. 7 



(if the Echiiioidea, the PourtalesiadcE excepted. Thus, of the 

 priniordial plates, fig. .9, the I a, II a, III i, IV a, Y h are 

 distinctly larger than the I h. [I />, III a. IV 6, V a, while 

 in each of the live second pairs the plates of the former se- 

 ries are less advanced than those of the latter. From these 

 iuecinalities there arises, at this early stage. a deviation from 

 tlie eircnlar disposition more obvious in tlie dextral half, 

 1 a — III a, and caused by the detached II a pressing oii 

 the point of eontact between the interradium 1 and the small 

 IV a. 



The interradial plates are liexagonal, somewhat bi'oader 

 than they are high, large, convex. each provided Avitli a pri- 

 mary, distinctly perforated verrnca. They are all contiguous 

 within every column. Every interradinm consists of four pairs 

 (if alternating plates and one primordial, peristomal plate, 

 liroad and well-developed, fifj. .9.' This solitary adoral is ex- 

 (Inded from the tlrst and innermost coronal circle, but enters 

 into the second. which consequently comes to be formed of ten 

 second binar}^ ambnlacrals and live primordial solitary inter- 

 ladials. This is tlie normal constitntion of tlie peristome in 

 the whole class. 



The space encircled by the adoral ends of the ten primary 

 ambnlacrals, in the centre of which the lip will come to snr- 

 ronnd the fntnre month, is at this stage closed över by the 

 covering membrane. In the dried specimen, fig. .9, this has been 

 dravvn in into the opening. It is transparent and from nnder 

 the adoral ends of the priniordial ambnlacrals are seen pro- 

 trnding those of the pyramids, tlie two halves of each ronn- 

 ded. interradial. bnt no teeth are visible. 



One of the less advanced specimens, the same which af- 

 forded the fig o, was cut open horizontally so as to show the 

 alimentarv caiial. the intestine proper, the (rsophagns and the 

 rectnin. FL III. fig. 10, 11. 1^. The intestine is snspen- 

 ded över the still Hatly expanded dental apparatns, fig. 11, 

 and has the shape of an oblong bag bent npon itself almost 

 horizontally into a pentangnlarly eircnlar form, fig. 10. the 

 middle of its great cnrvatnre answering to the sntnre V, 4, 

 while the somewhat narrowed terminations nieet iiear the su- 

 tnre II, i. Its dorsal snrface. fig. 10. is convex, even, not 



' First observed bv Döderlein, Japanische Seeigel, p. .'52. Pl. IX. fig. <>, 



p. r. 



