UNIVALVE MOLLUSKS 127 



that lives in the south. Its shell is thin, white, and 

 ornamented with numerous fine ridges running from 

 the apex two-thirds of the whole length. The aper- 

 ture 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. It has been dredged 

 off San Pedro by Mr. H. N. Lowe, along with other 

 rare species ot shells. 



Cadulus liepburni^ Dall, Hepburn's Tusk-shell, is 

 found near the city of Victoria, B. C. It is onl)^ 1 1 

 mm. in length, and is polished, white, and nearly 

 straight. Cadulus tolmiei^ Dall, Tolmie's Tusk- 

 shell, is found with the last species, but it is more 

 curved, and rapidly tapers. Cadulus aherrans^ 

 Whiteaves, the Wandering 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 light and 

 thin, and in modern times at least, they are quite 

 small. A few have been found on our coast, nota- 

 bly, 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 longest. It has come ashore in southern 

 California, and perhaps elsewhere. 



At this point we will describe a few odd mollusks 



