UNIVALVE MOLLUSKS 113 
ering. This species is found sparingly upon 
mossy rocks on the southern coast. 
In 1863 three large specimens of Aplisia cali- 
fornica, Cooper, the California Sea-hare, were re- 
ported as found on San Pedro beach after a storm. 
One of them was fifteen inches long and five in- 
ches wide. Their stomachs were full of seaweed. 
The sea-hares are singular creatures, being long 
and slug-like, with a distinct head, while the rudi- 
mentary shell is concealed by the mantle. Not- 
withstanding their somewhat offensive appear- 
ance they are perfectly harmless, and may be 
handled with impunity. 
Pleurobranchus californicus, Dall, the Califor- 
nia Side-gill, also comes from San Pedro. The 
animal is oval and flattened and has a distinct 
head. The shell is a thin, white scale, concealed in 
the mantle. The gill is single, free at one end, 
placed on the right side between the mantle and 
the foot. The animal is waxy white in color, about 
an inch long, while the little shell is half of that 
length. 
Somewhat similar in their anatomy to the last 
few species are the Sea-slugs, which form a great 
group of naked mollusks. While they have no 
shells, they are far from being without interest. 
Their bodies are often very brilliantly colored, so 
that when they are alive and swimming they are 
among the most beautiful objects of the sea. You 
will find them on seaweed at low water, looking 
like little lumps of soft tissue without form or 
beauty; but when put into a jar of seawater they 
