MOLLUSCA. 25 
state, high on the leaves of the Water Flag, having retired 
from the moisture below. In the same manner, and from 
causes equally obscure, some of the marine shelly mollusca, 
as the Limpet, Periwinkle, and Trochus, may be observed 
in a quiescent state on the rocks, above the reach of the 
tide. A shower, however, in general excites the Succinea, 
as well as the Limpets and Periwinkles, to motion. 
