PIERCED SHELLS AND CHITONS 



251 



Fig. 250. X i 



A greatly re- 

 duced view of 

 Lucapina crenula- 

 ta, Sby., the Great 

 Keyhole-limpet, is 

 shown in Figure 

 250. This is by 

 far the largest and 

 finest of the Ameri- 

 can Fissurellidse. 



Though this shell is often over four inches in length, 

 the animal is much longer, and somewhat resembles 

 a brick, both in shape and size. It has a huge yellow 

 foot, and a black mantle that nearly conceals the 

 white shell which rests upon the animal's back. The 

 edges of the shell are covered by a fold of the man- 

 tle, and its true size is not shown until this fold 

 is dissected away. 



This fine shell is marked with many radiating ribs 

 and concentric lines of growth. It has a large, ob- 

 long hole to one side of the center, around which, 

 internally, is a thick rim of enamel. The crenulated, 

 or scalloped, edge of the shell is a marked feature, 

 and suggested its specific name. Internally the shell 

 is of a pure glossy white, but the outside is some- 

 what dingy. This great mollusk is seldom found 

 near the shore, as it lives below the tide-mark, and 

 it must ordinaril}^ be gathered by dredging. 



Lucapinclla calliomarginata^ Cpr., the Southern 

 Keyhole-limpet, is a small species, living below tide- 

 mark, and is occasionally found from San Pedro 

 southward. The shell is low arched, with a rather 



