TOPS AND TURBANS 229 



naUculatum^ Mart., an enlarged view of which is 

 shown in Figure 223. The shape of this shell is 

 strictly conical, and the flattened whorls are girdled 

 with deep spiral channels, which lie between raised 

 ridges. The surface is ash-colored, though the shell 

 is rainbow-tinted within. The thin exterior layers 

 may very readily be removed by a weak acid if one 

 wishes to examine the deeper structure of the shell. 



Figure 224 presents to us another 

 shell of this genus, CaUlostonia costa- 

 tum. Mart., the Blue Top-shell. This 

 species is smaller than either of the 

 preceding members ot the genus, and it 

 lives nearer the shore. Hence we Fig. 224" 

 should naturally expect to find that it 

 had a thicker and stronger shell than the others, 

 and in this we are not disappointed. It has four 

 rounded whorls, marked with hne spiral ridges. 

 The thin, reddish brown outer coat is readily re- 

 moved, showing the blue pearly layer underneath. 

 This process is often accomplished naturally, and 

 broken shells especially show more or less of the 

 blue coloring, especially round the apex. 



I have found very fine living specimens hanging 

 from the roof and walls of a rock grotto after it had 

 been left empty of water by the retreat of the early 

 morning tide. I have also gathered them from the 

 long seaweeds that grow near the rocky shore. The 

 length of one of these shells is three-fourths of an 

 inch. The horny operculum is perfectly circular, 

 and the aperture of dead shells is often inhabited by 

 a thin variety of the White Slipper-shell. 



