UNIVALVE MOLLUSKS 107 
ning from the apex two-thirds of the whole length. 
The aperture is circular. 
Cadulus quadrifissus, Cpr., the Four-slit Tusk- 
shell. This very large name belongs to a very 
small shell, only half an inch long, which may be 
easily distinguished because the small end is cut 
by a little cross, composed of four slits. 
Cadulus hepburm, Dall, Hepburn’s 'Tusk-shell, 
is found near the city of Victoria, B. C. It is only 
11 mm. in length, and is polished, white, and nearly 
straight. C. tolmiei, Dall, Tolmie’s Tusk-shell, is 
found with the last species, but is more curved, and 
rapidly tapers. The shell is smooth, polished, and 
is 12 mm. long. C. abérrans, Whiteaves, the Wan- 
dering Tusk-shell, is the only other species of this 
genus found in the same locality as the last two. 
Its shell is larger and more curved. 
The Pteropods are mostly deep sea creatures, 
which live near the surface, and they have been 
well called ‘‘Sea-butterflies.’’ The shells are very 
thin and hght, and in modern times at least they 
are quite small. A few have been found on our 
coast, notably, Cavolinia tridentata, Forsk., the 
Trident Sea-butterfly. This little shell is thin, 
hollow, horn-colored, shaped like a small button 
with three small projections or points at one end, 
of which the middle one is the longer. It has come 
ashore in southern California, and perhaps else- 
where. 
A few years ago I visited the pretty little town 
of Bolinas, situated on the first bay to the north of 
the Golden Gate. From the shore there runs out 
