245 



The elegant markings with which the flat surfaces of these bodies are 

 adorned, are, like those on the surfaces of the trochitae, calculated to 

 form an appropriate articulation with the surfaces of other similar 

 bodies. By the union thus obtained, are formed those pentagonal 

 columnar bodies, which are generally known as columnar star-stones, 

 mAsterice Columnar es, and by some as angular stellated entrochi, (En- 

 trochi Angular es Stdlati.) 



These columns derive a considerable degree of variety, from the 

 difference, in structure and size, of the asteria3 of which they are 

 composed, as well as from the order in which they are arranged ; 

 their external markings, therefore, differ considerably. These diffe- 

 rences have been very accurately described by Rosinus, and shall be 

 here noticed, as closely as appears to be necessary. 



In some, as in Fig. 52, the constituting asteriae are of a similar 

 size and form : the line of articulation is therefore at the same dis- 

 tances through the whole column. See Rosinus also, Tab. IV. B. 1. 

 But in those columns which are formed of asteriae of different thick- 

 nesses, a correspondent difference in the distances will be observable 

 in the lines of articulation , since these will be more or less frequent, 

 as the asteriae are thinner or thicker: their lines of articulation will 

 also be more or less undulating, as theasteria3 are more or less grooved 

 on their sides. 



Fig. 48 and 53, consist of thicker and of thinner columns of aste* 

 riae, alternately disposed. Fig. 49 is formed by the thicker asteriae so 

 ranging with those which are thinner, and with those which are of the 

 thinnest kind, that between two of the thicker are placed two of the 

 thinnest, between which is placed one of a medium thickness. Rosi- 

 nus describes several varieties of this species, depending merely on the 

 different degrees of thickness in the thinnest asterras, and in the de- 

 grees of fineness in the crenulated markings in the line of articulation. 



Fig. 51 represents a columnar series of round asteriae, and composed 

 of thick, less thick, of thin, and of the thinnest asteriae, so disposed, 



