MARINE 
UNIVALVES 171 
Fig. 163 (*) 
Whelk, are shown in Figure 163. The left-hand 
ig. 164, x $ (*) 
figure represents the nor- 
mal form of this large 
shell, while the other is a 
picture of the form with 
three ridges, which 1s 
known as var. tricarin- 
dtum, Dall. Both shells 
have a translucent, brown 
outer coat, and = are 
marked with fine spiral 
lines of sculpture. 
Biccinum pléctrum, 
Stimpson, the Lyre Whelk, 
is shown in Figure 164. 
The shell is distinguished 
by ridges, which suggest 
