PURPUHA. 187 



are turreted and more or less distinctly ribbed. In early 

 stages, as seen on the upper part of the spire, the ribs are 

 adorned with scalloped leaflets, and sometimes this beauti- 

 fully-foliated structure is continued in the more adult con- 

 dition. The animal is of a yellowish tint or white, with 

 conspicuous eyes placed at the end of the bulging parts of 

 the tentacles ; the scalloped edges of the mantle correspond 

 with the denticulated edge of the aperture. 



The egg-bags of the Purjmra lapillus, commonly called 

 the ' dog periwinkle,' are deposited on the surface of rocks, 

 or stones, or shells, united in considerable numbers to a 

 common membrane, on which they stand erect like so many 

 oval cups, each cup containing an embryo. Here the young 

 Purj)iirce remain for some months before the cup opens; 

 and when this happens, they do not all take immediate ad- 

 vantage of the new-born privilege, but some of them prefer 

 remaining in ease and comfort where they are for a time, 

 till they acquire sufficient strength and courage to leave the 

 protection of their cells. 



The Ptirjmra, like the Littonnce, crawl about on the 

 shore between watermarks, and seldom venture under the 

 lower tidemark. GHding stealthily among the seaweeds 

 and stones, it seeks its prey, and woe to the small winkle, 



