SHELES Without, CANALES 219 
marked with sharp, spiral ridges, about twelve of 
which may be seen on the body-whorl. The outer 
hp is thin, and the umbilical chink is small. Its 
length is 8mm., and it is 7mm. in breadth. 
A series of river-shells now claim our attention. 
In general they are black, horn-shaped, and rather 
thin. Their inhabitants are dark-skinned, happy 
creatures, that love to live in cool, clear water, 
where the green alge grow and the banks are edged 
with ferns and water weeds. I gathered them in 
abundance from a little stream of most delicious 
water that bursts out from the base of a dry hill, 
just north of the village of Sisson, in northern 
California. Evidently there are concealed pas- 
sages leading from the dry hill up to the great 
snow fields on the flanks of Mount Shasta, for after 
you have climbed far up beyond the timber line 
and are walking over the great expanses of white 
you can hear the gurgling of little streams under 
your feet, and you know that the melting drifts are 
sinking down into the bosom of the mountain to 
reappear among the groves and meadows that 
mark the boundaries of the upper Sacramento. 
Gonidbasis plicifera, Lea, the Plaited 
River-shell, Figure 237, is a fine example 
of the shells of this group. It is easily dis- 
tinguished from the other species of the 
River-shells by the folds, or plications, on 
the whorls, especially upon the upper ones. 
It is essentially a northern form, living in 
the streams of Oregon and adjacent ter- 
ritory. 
Fig. 237 
