GASTEROPODA. 



289 



The Coat-of-Mail shells (Chiton} are of very remark- 

 able structure ; their body 'is covered by eight over- 

 lapping shelly plates, surrounded 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 such, that they are 

 enabled to roll themselves 

 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 with a shell, and breathing by 

 means of branchiae, placed upon their 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 



FlG. 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, jextrernely interesting- 

 objects, as the animals keep extending and with- 



* Nudus, uncovered ; branchiae, gills naked-giUed, 



O 



