ITS SKELETON. Ill 



normally three small plates, of which the middle one 

 is a little larger than the others. This regularity, 

 however, of arrangament is not always perfectly 

 maintained. All the plates, though very thin and 

 delicate, are roughened on hoth surfaces with minute 

 tuberculous knobs, set in rows in quincuncial order 

 (See Plate V., fig. 5), which near the edges run into 

 one another, and make small ridges. In looking at 

 this structure I was reminded of the spieulie of Alcy- 

 onium, &c., which are roughened with similar knobs ; 

 and though the latter are only minute atoms imbed- 

 ded in the flesh, they are doubtless the rudimentary 

 representatives of these stony plates. 



The interior edges of the plates form a deep cup, 

 at the bottom of which they meet. The central one 

 of the three intermediate plates, or what has been 

 called the second cycle, sends oft' another plate into 

 the hollow of the cup, which is similar in form to 

 those of the circumference, but much smaller, the top 

 not rising to nearly their level. The centre of the 

 cup is occupied by a series of slender frilled and 

 irregularly twisted plates, forming a spongy mass, the 

 top of which is still lower than the level of the sub- 

 ordinate circle of plates. 



This is but the skeleton ; and though it is a very 

 pretty object, those who are acquainted with it alone, 

 can form from it a very poor idea of the beauty ot 

 the living animal. When we take it from its attach- 

 ment and remove it from its native element, the 

 violence causes it to contract so forcibly, that vou 

 would see nothing but what I have described, and 

 would scarcely perceive any difference between it and 



