246 Proceedings of the Royal Society of Edinburgh. [Sess. 
appeared (Plate, fig. 1). The peristome and mouth parts were normal, 
but in the apical system abnormality was strikingly apparent. The 
genital plates of areas 1, 2, and 3 (the last split into two segments) were 
present approximately in their normal positions, and associated with them, 
in the customary arrangement, were the oculars I., II., III., and IV. It is 
certainly remarkable that in spite of the spreading out of the plates 
surrounding the periproct not one of the oculars was “ insert.” The 
remainder of the periphery of the periproct was bounded by a single rank 
171 - 
Fig. 2. — Incomplete Development in Echinus esculentus. Apical area and surrounding 
coronal plates x 3 ; gen. 5, supposed 5th genital plate. 
of small plates, each more or less rectangular in outline, with several 
smaller triangular plates thrust in to complete the almost circular outline 
of the series. This abnormal series contained in all nineteen plates and 
demi-plates, with two additional small circular plates between ocular I. 
and the margin of the periproct. The plates were similar in size and 
shape, and the majority bore primary tubercles, but one, the third from 
ocular I., was perforated by a distinct pore and possibly represents genital 5, 
although in the dried state no genital products were associated with it. 
The madreporite was divided into two lobes, both perforate. 
Outside the ambulacral area the derangement and consequent regulation 
was exceedingly extensive. Apart from the one disturbed area, the 
