NORTH-CAROLINA GEOLOGICAL SURVEY. 



has received the name of Test, or Shell. The patterns- of these 

 different areas vary in form and proportion, and hence are 

 used as characteristics of genera and species. The test is also 

 covered with spines of different forms and sizes. These, too, 

 are formed after different patterns, their shafts being sculp- 

 tured differently in every species. Their spines, and the 

 mode they are attached to the shell, the character of their 

 surfaces, the position of their oral and excretory orifices, fur- 

 nish the characters upon which the families, and lesser sub- 

 divisions of this class are founded. 



FAMILY CIDARIDAE. CTDARIS MITCHELLII. N. S. (Fig. 237.) 



Test thick, circular or turban shaped ; flattened above and 

 below; ambulacral areas narrow, and provided only with 



minute tubercles, in double rows, 

 FIG. 237. and three in each ; interambulacral 



areas nearly four times as wide as 

 the former, and furnished with two 

 distinct rows of large primary tu- 

 bercles, with about eight in a row, 

 including the smaller ones upon the 

 disks; tubercles perforated; inner 

 rim surrounding the tubercle, 

 smooth ; outer, bearing small sub- 

 ordinate spines, giving it a crenulated appearance ; miliary 

 zones wide, and covered with small close set unequal granules ; 

 poriferous zones, unigeminal, and separated by nearly plane 

 ridges ; spines unknown ; apical disk unknown ; mouth open- 

 ing, appears to be large, but too much broken to determine 

 its characters. 



Belongs to the eocene, and accompanies the remains of the 

 Zeuglodon. 



Dedicated to the lamented Prof. Mitchell of the University 

 of Chapel Hill. 



CIDARIS CAROLINEN8IS. N. S. (Fig. 238.) 



Test rather thick, circular and somewhat oval. Ambulacral 

 areas narrow ; somewhat undulating, supporting two row* of 

 21 



