43 
LEPAS. 
Section A. Sessile. (See Plate III. Fig. 2.) 
B. Peduncled. (Fig. 3.) 
Shell multi valve ; affixed by the base; valves 
unequal, erect. 
In the first division of this genus, the species 
have mostly 6 valves, are conical, adhere by their 
base to rocks, shells, &c. In the second they are 
compressed, varying in number, supported by a pe- 
duncle or hollow membranaceous stalk. ^ The for- 
mer have also an operculum composed of 4 or 6 
triangular valves closing internally the vertex of the 
shell, and affixed by an elastic cartilage to the in- 
terior of the upper margin. The cellular structure 
of these shells is worthy of observation : the hol- 
low striae and cavities of the triangular valves are 
vertical, and the space between them is filled with 
nearly horizontal filaments, forming a more com- 
pact and even substance. The two divisions of 
this genus, though appearing, at first sight, ex- 
tremely dissimilar, are yet congeners in their prin- 
I 
