66 THE NAUTILUS. 



above locality also, square yards of surface of some of the flat 

 rocks being filled with its shells. This species seems to abound 

 from San Pedro, Cal., to Magdalena Bay, Baja Cal., where I 

 found millions of the young shells in the drift (determined by 

 Dr. Dall). 



Acmaea patina cumingii. This is the commonest species at 

 Bird Rock and all along our coast, but seems to have been over- 

 looked by Smith and Bailey. 



Tegula ligulatum. One of the commoner shells on all our 

 beaches. 



Pecten hastatus. In kelp holdfasts washed ashore at Pacific 

 Beach. 



Pecten hericeus. Valves frequent in the drift. 



Phacoides calif 'ornicus. Frequent in the drift on all our 

 beaches. 



Phacoides richthofeni. Valves occasionally washed ashore. 

 Mr. Emery found it living in False Bay. 



Fissurella volcano. This is probably one of the most abundant 

 and widely distributed species on our coast. I have generally 

 looked with contempt on the gathering of dead shells; but for 

 lack of better material I have gathered several thousand of this 

 from the drift, from very minute to specimens of maximum 

 size. It occurs from Monterey, Cal., south at least as far as 

 Salina Cruz, Oaxaca, where I have collected it in abundance. 

 The beach-worn shells show a beautiful diversity of color not 

 observable in the living shells. About fifteen per cent, of the 

 shells picked up at La Jolla are of the var. crucifera Dall, some- 

 times the arms of the cross extending only halfway down the 

 sides of the shell, sometimes wholly worn away at the apex, 

 often one or more arms missing; in young specimens, say 2 mm. 

 long, frequently only the lateral white arms appear halfway to 

 the lower margin of the shell. The ground work is usually 

 reddish, the gray or black forms being much rarer. From the 

 four white arms . x f var. crucifera there occurs every variation in 

 number up to 20 01 30 or more, the red rays on a white ground 

 like red-hot lava flowing down the sides of a mountain, hav- 

 ing given it its name. This is probably the typical form. 



Acmaea triangularis. One specimen detected in the drift on 

 the beach. 



