103 



Explanation of the Plates. 



Tab. I. 



Fig. 1. A very young 10-armed specimen of Brisingacoronata, seen from 

 above, natural size; on the left there appears a recently regenerated arm. 



Fig. 2. The disc of the same specimen, with the base of 4 arms in their natural 

 connexion, viewed from below, somewhat magnified. 



lig. 3. The same viewed from above: b, the madreporic body. 



Fig. 4. The disc of a full grown 9-armed specimen viewed from above, very slightly 

 magnified: a, the secretory pore; b, the madreporic body; c c, the radial spaces of the 

 disc; d d, the iuterradial spaces, with the wedge-plate inserted in the angles of the arms; 

 e, a recently regenerated arm. 



Fig. 5. The same viewed from below: c d e, as in the preceding figure; f, the 

 oral aperture strongly contracted. 



Fig. 6. The same viewed from the side. The letters as in the 2 preceding figures. 



Fig. 7. A piece of the dorsal skin of the disc, with the secretory pore (a) more 

 strongly magnified. 



Fig. 8. Perpendicular section of the dorsal skin of the disc, still more strongly 

 magnified, shewing the 2 layers of the skin, the spines with their cuticular sheaths (b) and 

 the pedicellaries (a). 



Fig. 9. A single disc-spine with the basal plate belonging to it, strongly magnified: 

 a, the basal plate contained in the dorsal skin; b, the spine itself; c, its cuticular sheath. 



Fig. 10—11. Various forms of dorsal spines. 



Fig. 12. An arm of a full grown specimen, viewed from the side, natural size: 

 a, the left genital aperture; b, the dorsal marginal plates at the base. 



Fig. 13. A piece of the same about in the middle of the length of the arm, viewed 

 from the side, slightly magnified: 1, marginal spine; 2, 3, furrow-spines. 



Fig. 14. The same piece viewed from below. The water-feet are removed, with 

 exception only of 2 pairs: 1, marginal spine; 2, 3, 4, furrow-spines; a, water-ieet. 



Fig. 15. A marginal spine, magnified, and treated with a solution of potash, whereby 

 the cuticular sheath has been rendered transparent. 



