100 WEST AMERICAN SHELLS 
Lyonsiélla alaskana, the 
Alaska Lyon-shell, is shown 
in Figure 89. The specimen 
was dredged from deep wa- 
ter in the Gulf of Alaska. 
The figure is somewhat en- 
larged, but it shows the main 
external features of this thin 
and delicate shell. 
Mytiliméria nuttalli, Conr., 
the Sea-bottle Shell, is a singular mollusk, which 
may be found imbedded in a colony of compound 
Ascidians, or Sea-bottles. The shell is very thin, 
white, and is covered with a brown epidermis, and 
there is an oscicle under the hinge. In shape the 
shell resembles an inflated bladder, with the spiral 
beaks at one end. Its height is about one inch. 
This is a singular instance of a thin shell deriving 
protection from the bodies of the animals by which 
it is concealed. 
Our next species is named Hntodésma saxicola, 
Baird, the Rock Entodesma. It is a singular crea- 
ture, living in holes of various shapes and taking 
whatever form seems most convenient. The shell 
is somewhat oblong or pear-shaped, bulging at the 
hinge end, gaping beneath, and prolonged around 
the siphons into an irregular process consisting 
chiefly of epidermis. Internally the shell is white, 
while externally it is very rough and unsightly, 
being partly covered with a brown periostracum. 
When dry it is usually more or less bent or broken, 
owing to the unequal shrinkage of the hard parts 
Fig. 89, x 3 (*) 
