CALLIOSTOMA. 8l 



Fig. 66 presents to us another shell, Calliostoma 



costahun^ Mart. This species is smaller 



than either of the preceding members of 



the genus, and lives nearer the shore. 



Hence we would naturally expect to 



find that it had a thicker and stronger 



shell than either of the others, and in 



Fig. 66. this we are not disappointed. 



It has four rounded whorls, marked with fine spiral 



ridges. The thin, reddish brown outer coat is readily 



removed, showing the blue pearly shell underneath. 



I have found very fine living specimens, hanging 



upon the roof and walls of some rocky grotto which 



had been left by the early morning tide. I have also 



gathered them from the long seaweeds which grow 



near the rocky shore. 



The length of one of these shells is about three- 

 fourths of an inch ; the operculum is thin and per- 

 fectly circular; the aperture of dead shells is often 

 inhabited by a thin variety of the White Slipper- 

 shell. 



The above mentioned three species are the most 

 common representatives of the group, but there are 

 several others, some of which are not less beautiful, 

 though they are more rare. The names given to 

 them indicate their special characteristics. 



Among them we find Calliostoma gemmidatum^ 

 Cpr., jem-mu-la^-tum, in size like the last, but more 

 acute in form. Each whorl has two principal rows 

 of granules, with some smaller markings. The 

 whorls of this southern species are very distinct, and 

 its color is gray, with dark cross-stripes running 

 down from the apex. 



(6) 



