GASTEROPODA. 



289 



Tlie Coat-of-Mail shells (Chiton) are of very remark- 

 able structure ; their body is covered by eight over- 

 lapping shelly plates, surroimded by a tough leathery 

 margin, often studded with 

 little scales or spines or hairs, 

 under the protection of which 

 the branchiae are situated. 

 The flexibility of their ar- 

 mour is sucli, that they are 

 enabled to roll themselves 



• , 1 11 1 xi • 1, J Fig. 229.— tufted tkitos. 



up into a ball, and their head 



is quite unprovided either with eyes or tentacula. 



Order Nudibranchiata.* 



The animals belonging to this order are marine 

 slugs, unprovided witli a shell, and breathing by 

 means of branchiae, placed upon tlieir backs, and thus 

 exposed, naked, and unprotected, to the influence of 

 the surrounding medium (Fig. 230). 



Several species of these naked-gilled Mollusca are 

 common on the British coasts. They exhibit a very 

 great diversity of form, and an extraordinary variety 



Fig. 230.— crowned eolis 



of lively and beautiful colours. The gills are con- 

 tractile into cavities on the surface of the body, and 

 present, in the living state, extremely interesting- 

 objects, as the animals keep extending and with- 



* Nudiis, uncovered ; branchiae, gills — nahed-gilled. 



O 



