71 CALAMOCRINUS DIOMEDjE. 



reach the ambitus. The figures of Pholidocidaris on Plate 15, Fig. 9, of 

 Vol. \'.. are from specimens so badly crushed that the original arrangement 

 can no longer be detected ; and Hall's figures of Lepidechinus in the 

 Geology of Iowa, Vol. 1.. Part 2, Plato IX. Fig. 10, show three or four 

 plates at the actinal edge. 1 do not understand Loven when he says,* 

 speaking of the Palaechinidse, that the adambulacral plates alone attain to 

 the peristome and to the apical system, and I cannot agree with him when 

 he gives this as a character of the order of Perischoechinidaj in his 

 Etudes, p. 39. 



Neumayer points out that in Cidaris coronata there are ten alternating 

 plates forming two regular circles within the anal area, and nothing that 

 is known of the youngest Cidaridae indicates that this is not the normal 

 number of plates; so that, if there has been a single anal plate in very 

 young stages, it must have disappeared early. 



If we examine other Echini still younger geologically, and pass to the 

 . I ura. we find in the Cidaris of those days an arrangement of the apical 

 plates almost identical with that of the Palaechinidaa, — an arrangement 

 which still exists among the Cidaridae of to-day.f 



In the young Cidaridae there are five larger anal plates separating the 

 ocular from the genital plates, and the central space is filled with minute 

 plates. These five radial plates always retain their prominence in the full 

 grown Cidaris. and have as good a right to be considered as infrabasals as 

 the plates considered as such in the Ophiuridae and Starfishes by Carpen- 

 ter and Sladen. See Plate II. Figs. 2, 17, and Plate IV. Fig. 2, of my 

 Report on the " Blake " Echini. t 



The anal plates in the Cidaridae are not, as is stated by Carpenter, the 

 remains of the central disk together with numerous secondary anal plates. 

 There is nothing known to prove that in the Cidaridae the anal system 

 is not in the earliest stages covered by five plates, as in the Arbaciadae it is 

 covered by four, or in exceptional cases by five. We can scarcely speak of 

 the subanal plates in young Echini as being in their primitive condition 

 of " a fairly regular pentagonal shape." This can hardly be stated of any 

 young Echinus I have had the opportunity to examine, (see sundry figures 



* Pourtalesia, p. 11. 



t As, for instance, in Phyllacanthus baculosa (Plate XXIX. Fig. 7), in Goniocidaris geranioides 

 (Fig. 0) and other species of Goniocidaris (Figs. 3, 4), and in "Several species of Dorocidaris (Figs. 



S-lL'). 



t Mem. Mas. Comp. Zool., Vol. X. No. 1. 



