c ILAM0CRIN1 S DIOMED l 7:; 



evident thai these bo exiled pores are only perforated tubercles, or the 

 pits left after the minute radioles bave been broken off The bo called 

 genital plates are not perforated, and the body whicb Schmidt calls madre- 

 poric can hardly be considered as such, as it is in the ambulacrum. (See 

 also Plate XXIX. Fig. 1. of this Memoir.) Bui the apical sj'stem of B. globu- 

 lus which he figures is evidently most irregular, and perhaps abnormal. 

 Schmidt's description of the apical system of B Pahleni does not agree 

 with the figure which he gives on Plate IV. Fig. l b , one of the smaller 



triangular apical interaiuhulacral plates which separate the radial plates 

 1,2, is not figured j though he speaks of live smaller triangular pieces, he 

 figures only lour. 



In the figure given by de Koninek* of Palaechinus sphaericus, four of the 

 genital plates are similar, eight-sided with three pores, and one seven- 

 sided with only one pore ; he could find no trace of the ocular plates. 

 These I imagine must have been very diminutive. The apical part of the 

 tost which he figures shows at the apex only two rows of interambulacral 

 plates in contact with the genital plates, occupying practically the same 

 position as in the regular Echini; so that, owing to the shape of the 

 plates, we have, as with them, one small and one large plate, the first 

 plate being the youngest, and the next two forming obliquely the second 

 tier. Next come three, and finally four rows, the second and third rows 

 of interambulacral plates being intercalated as it were between the outer 

 rows. — an arrangement which is more or less distinct in genera with but 

 four or five rows of interambulacra, but is difficult to trace where there 

 are more. But they all agree in having one or two rows of interambulacral 

 plates next to the apical and actinal systems. 



In the figure given by Bailey t of the abactinal system of Pahvchinus 

 elegans (see also this Memoir, Plate XXIX. Fig. 2), three, or rather four, 

 of the infrabasals may still be seen in their proper place. 



I am astonished at the statement which Loven makes regarding the struc- 

 ture of the interambulacra at the ambitus in PalaechinidaB. In none of the 

 figures which he quotes is there such an arrangement at the actinostome 

 as that he gives as characteristic of the order. Meek and Worthen's fig- 

 ure of Melonites (Palsfiont. of 111., Vol. II. p. 227, Fig. 21) shows two and 

 three plates, and their figure of Oligoporus (p. 248, Fig. 27) does not 



* Bull. Acad, de Brux., XXVIII.. p. 544. Plate. Fig. 1. 



f Plate IV. Fig. B, Journal Royal Geol. Soc. of Ireland, Vol. I., New Series, 18C4-67. 



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