OLIVE SHELLS. 
23 
bles the last, but is much smaller, being only 
three-fourths of an inch in length. Its whorls are 
beautifully: rounded and cut into little squares. 
Shell, thin, light brown, with a trace of orange 
inside. It is found from San Francisco Bay, 
southward. 
JY asset- mendica , Gld., Fig. 4, PI. IV, is a vari- 
able shell, about the same in length as the last, but 
more slender. The surface is marked with fine 
spiral lines and numerous transverse ribs. Its 
color is light brown, with a white “ peristome,” 
or margin of the aperture. Fine specimens of 
this species have been found at Santa Cruz and 
Monterey. 
Nassct Cooperi , Fbs., Cooper’s Basket-Shell, 
shown in Fig. 5, PL IV, is a pretty, brownish 
little shell, found from Bolinas Bay to San 
Diego. It is spirally marked, like N. mendica, 
but its ribs number only seven or eight to a 
whorl, and are quite high, giving the shell a 
tubercled appearance. The white lip is marked 
internally with small teeth. 
AVe now come to one of the beauties of our 
Coast, the Purple Olive, Olivella biplicata , Shy. 
Fig. I, PI. IV. Every one must admire its blu- 
ish-white, polished surface, and purple mouth. 
The spire is short, with a distinct spiral groove 
separating the whorls. The inner wall of the 
aperture is marked by a bulge of enamel above, 
and two small folds beneath, which give the 
shell its specific name. Beds of living Olives 
can sometimes be found just beneath the surface 
of the sand, at low tide. They are active little 
burrow^ers, throwing up little ridges as they 
