246 



that one of but medium thickness is placed between two thin ones, 

 which, again, are comprised between two of more than ordinary thick- 

 ness, the thinnest of all being interposed between each of the pre- 

 ceding articulations. Round the thickest of these asteria3 are placed 

 five little pits, evidently intended for the insertion of lateral pro- 

 cesses. 



From similar changes in the arrangement of pentagonal asteriae ; 

 from the intermixture of those differing in thickness, and the disposi- 

 tion of their ornamental protuberances, great variety arises. Some 

 specimens are figured by Rosinus as being remarkable, from their as- 

 teriae being joined together in an anomalous manner; the lines of ar- 

 ticulation, in some, assuming somewhat of a spiral twist ; whilst in 

 others, additional lines appear irregularly to intersect and divide 

 the asteriae in various directions. Some of these differences appear 

 to be the effect entirely of injury from violence, inflicted either dur- 

 ing the life of the animal, or whilst passing from the animal to the 

 mineral state ; but others may properly be regarded as sports of na- 

 ture. 



The sides of the asteriae, forming the column, Fig. 54, is marked on 

 its sides by transverse lines of points, gradually diminishing in size, 

 from the centre of the line, and differing in their length, and even their 

 arrangement, in different columns. In the column, Fig 55, each star- 

 stone is adorned by a line of minute projections, placed on each angle 

 of the star, and extending each way about one-eighth of each side. 

 The whole surface of the column is thus made to assume a richly em- 

 bossed appearance, to which the conspicuous appearance of the cre- 

 nated line of articulation much contributes. 



The column, Fig. 56, has a still more elegant appearance. The pat- 

 tern of its ornament may be seen to comprise five of the asteriae ; the 

 uppermost, lowest, and most projecting of which are encircled by a 

 line, which swelling boldly in the middle of the sides, terminates ia. 



