LITTORINA. 



the most part gradually acuminated, sometimes very short 

 and obtuse ; aperture elliptical, rather acute at the upper 

 part, peritreme sharp-edged; columella rather flat; oper- 

 culum horny, spiral, consisting of few volutions, increasing 

 rapidly in width, its nucleus lateral. 



There are several fossil species, found in the tertiary 

 beds, and some others occur even as low as the Coral rag 

 and the Inferior Oolite. 



In our plate we have represented the following : 



Fig. 1. Littorina vulgaris, the common Periwinkle. 



2. pulchra, Turbo pulcher^ Sjwatnjon. 



3. — — its operculum 



4. varia, a new species from Panama. 



5. filosa, a new species from S. America. 



6. obesa, a new species from the South Sea Islands, 



