PUKPLES. 19 



to aperture run thirteen spiral grooves, giving it 

 the appearance of C. dims. It can easily be dis- 

 tinguished by its shorter spire, smooth lip, and 

 deep suture. It is of light color, sometimes streak 

 with reddish brown. 



Purpura crispata, Chem., Rough Purple, Fig. 

 0, PL II. is found in San Francisco Bay, but is 

 more common in more northern regions. It is 

 often two or three inches long, strong and heavy. 

 The spire consists of four strongly grooved 

 whorls. The body whorl is sometimes smooth, 

 but often very rough and foliated. It is said to 

 change the habit of its growth, when moved into 

 new localities. Its color is white or light brown. 

 In old shells, the umbilicus is conspicuous. Like 

 the other purples it has a horny, elongated oper- 

 culum. Fig. 1, PI. I, represents the same species. 



Next comes a genus of mollusks, almost pecu- 

 liar to the west coast ot America. A good rep- 

 resentative is shown in Fig. J , PI. HI ? Mono- 

 ceros lajnlloides, Conr., Pebbly Horn Shell. It 

 is so named on account of a little horn, near the 

 base of the outer lip. It is a pretty little shell, 

 found on the rocks between tides, having a spire 

 of four whorls, a rather small white mouth, set 

 with seven teeth. The outside is marked with 

 spiral grooves, and the lines of growth break up 

 the brown color into little blocks. The shells 

 are very thick and strong, well fitted to resist 

 the force of the waves. Thin and delicate shells 

 are generally found in deep water, where there 

 is little danger of being dashed against the rocks. 

 Shore shells are usually strong and solid. When- 

 ever you examine a shell, notice these points 



