228 Prof. P. M. Duncan and Mr. W. P. Sladen on the 



developed plastron and crescentic-shaped peristome of the 

 Kleinia show how greatly the forms differ. 



Gray termed his species Leshia mirabilis^ and this has very 

 properly become Paheostoma mirabile, Gray, sp. 



There are several excellent drawings of the apical system 

 of Palceostoma mirahile, Grray, sp., and the last given by Lov^n 

 is of course most worthy of study (' On Pourtalesiay &c., 

 plate xvi. fig. 190). Other plates equally exact are in 

 Loven's ' Etudes,' plate xii. figs. 103 and 104. In the 

 drawing on the first-mentioned plate, fig. 190, the remark- 

 able appearance of the two large generative pores situated on 

 prominent mamilliform projections is very distinctly rendered. 

 No madreporic plate is to be seen, and the right and left 

 anterior generative plates are not perforated by pores for the 

 ovaries. The drawing shows one perforation on the flank of 

 the right posterior ])late and another in the median line, but 

 in the riglit anterior plate; it is probable that these pores are 

 the feebly developed water-pores. Behind the mamilliform 

 projections there is a space without any signs of sutures, and 

 which is broad posteriorly, where it separates the posterior 

 ocular plates. 



In front of the mamilliform projections the riglit anterior 

 generative plate extends as a narrow and somewhat pointed 

 plate between the ambulacra, and the left anterior plate is of 

 the same general shape, but is smaller and not so pointed in 

 front. 



The drawing does not leave the impression that the mamil- 

 liform projections are situated upon keel-shaped elevations of 

 the posterior lateral interradia, Nos. 1 and 4. In the outline 

 figure, plate xii. fig. 103, of the ' Etudes,' the deficiency of 

 sutures in the rpical disk is almost as evident as in the finished 

 drawing just noticed. 



The only sutural line is that which separates the small left 

 anterior generative plate from the combined plates. There is 

 no plate penetrated by water-pores, and the amount of plate 

 behind the two mamilliform eminences is considerable. 



The figure 104 of the same plate of the ' Etudes ' is a view 

 from within of the apical system. It shows the two large 

 generative pores, the small left anterior generative plate, and 

 the united right anterior and right and left posterior plates. 

 But the right anterior plate has no pore or perforations, and 

 it passes backwards, pushing tlie large pores apart, and reaches 

 behind ihem and separates the posterior ocular plates some- 

 what widely. This figure is taken from a young individual 

 whose plates Loven notices are not distinct. 



The meaning of the view from within can be readily 



