CIDARID.E. 



renewed examination of the anal plates of a young Gomocidaris canaliculula 

 of 1.5 mm., Fig. 15, which I owe to Sir Wyville Thomson, shows that 

 in the youngest stages, about the size of that examined by Loven, there 

 are already five anal plates (PI. 13, fig. 6). 



Doederlein^ has figured a young specimen of D. canaliciilata showing the 

 primordial interambulacral plates. He ^ has also figured a young specimen 

 of X. verUcilJata showing the five primary anal plates witli one intercalated 

 plate. In a young specimen of Porocidaris Milleri of 14 mm. (PI. 7, fig. 6) 

 there are five large anal plates in the angles of their respective pentagons. 

 Fig. 16. Three of these are in contact and occupy the left part of the 



14 mm. 



Fig. 16. Porocidaris Milleri. 



18 mm. 



Fig. 17. Porocidaris Milleri. 



anal system, — the anterior plate and the left lateral plates. The two right 

 lateral plates are also in contact, but are separated from the next anal 

 plates by one and by two secondary anal plates which have reached the 

 genital ring, while three small plates have barely obtained a foothold be- 

 tween the other anal plates. The plates of the third series are only three 

 in number. 



The order of appearance of the second and third series does not seem to 

 be regular, as is clearly seen in other specimens of P. Milleri of 18 and 

 28 mm. In a specimen of 18 mm. (PI. 7, fig. 4) the three primitive anal 

 plates which are connected are not the same as those of the younger stage 

 just described, Fig. 17. They are in this larger specimen the two posterior 

 plates and the left anterior, while the odd anterior and the right anterior 

 are separated by single plates from the next adjacent series of anal plates 

 (PI. 7, fig. A)- 



Even in specimens of the same size the primitive anal plates and the 

 secondary anal plates which separate them and have reached the genital 

 ring are not the same. In a male of 28 mm. (PI. 7, fig. 1) the odd anterior 



* Japanische Seeigel PI. IX. fig. 6. 



^ Japanische Seeigel, PI. IX. fig. S a. 



