PLATES 21 AND 22. 



IlLUSTEATITE OF Me. MACKlIfTOSH's PapEK " Ox A ilALFOEilED CoEONA 

 OF ECHTNTIS ESCTJLEXTUS." 



Vide Proceedings E. I. Acad., Yol. 2, Ser. 2, p. 114. 



Plate 21. — Fig. 1. Abactinal aspect of corona. I., II., III., IV., Y., 

 genital plates. 1,2, 3, 4, 5, ocular plates. Plate I. is the madreporic ; 

 plate II. is seen to have lost its genital pore, a, right prong of ambula- 

 crum 2, stopping short a little above the ambitus. (In this ambulacrum, 

 in this and the next figuxe, the lithographer has in many instances 

 represented as dots what are really small tubercles, and thus the pores 

 seem much more numerous than they actually are), a', a group of 

 three or four pores belonging to ambulacrum a. a", pores belonging 

 to the left prong of ambulacrum a, which are placed inside the inter- 

 ambulacral plates of 11a. p, large central plate round which a number 

 of other plates are arranged in a radiate manner, s, a small perfora- 

 tion through the corona, apparently a hole produced by absorption. 



Fig. 2. Corona seen from left-hand side, a, a', as before ; h, actinal 

 boss. The point of bifurcation of ambulacrum 2 is seen near the 

 bottom of the figure ; also the remarkable " petaloid" appearance of 

 interambulacrum II., and the scattered arrangement of the pores in the 

 left prong of ambulacrum 2. 



Plate 22. — Fig. 3. Posterior aspect of corona, showing the remark- 

 able alterations which the plates have undergone. Eeferenees as 

 before. 



Fig. 4. Actinal aspect of corona, a, h, as before ; the line 5 termi- 

 nates on the summit of the boss. Ambulacrum 1 is seen to have a 

 very short course, tenninating a short distance beyond the top of the 

 boss. The bifurcation of ambulacrum 2a is seen to take place about 

 half way between the margin and the edge of the actinal orifice, the 

 whole of which is displaced downwards and to the right-hand side. 

 The sutures of the plates in the neighbourhood of the altered parts are 

 almost entirely obliterated. * 



All the figures are reduced to about nhe natua-al size. 



