68 THE NAUTILUS. 



Lucapina crenulata Sby. Monoceros lapilloides Com. 



Fissuridea aspera Escli. Olivellu boetica Cpr. 



Pachgpoma inequale Martyn. Oliva biplicata Sby. 



Pomaulax undosus Wood. Purpura saxicola Val. 



Ocinebra circurntexta Stearns. Mytilus californianus Con. 



Fusus barbarensis Trask. Haliotls rufescens Swain. 



Mitra maura Swains. Haliotis cracherodii Leach. 



Cancellnria cooperi Gabb. Haliotis corrugata Gray. 



Ischnochiton conspicuus Cpr. Natica sp. 



The reefs where the Acmaea gigantea have their liome, jutting out 

 between the sand beaches, are, after every storm, temporarily cov- 

 ered over with sand. At such times a large quantity of sand gets 

 under the mantle of the Acmcea, causing little nodules to be formed 

 on the inside of the shell, from the size of a pinhead to that of a small 

 bean. The shells were of unusual thickness, to withstand the con- 

 tinual pounding of the surf. 



As I have previously stated, the island is almost destitute of vege- 

 tation, making the land shells few and far between. The only species 

 were: Helix tryoni, found alive in small numbers; H. f emits, one 

 fresh specimen and occasional dead ones; H. sodalis, none but dead 

 and bleached ones. I should probably not have obtained any live 

 Helices had it not been for a rain storm which came on while I was 

 on the island, when the tiny creatures seemed to sprout as it were 

 from the bowels of the earth. After every rain storm there comes a 

 fierce, drying, west wind, which makes the snails "hunt their holes" 

 in a hurry, and any unfortunate Helix not under cover is made short 

 work of by the scorching winds and sand blowing upon them. About 

 the only food for the snails is a low-growing salt bush, at the roots of 

 which they burrow in the dry season. At the east end of the island 

 are found the few scattering live Helices with comparatively few dead 

 shells, while at the west end of the island the dead and bleached 

 shells lie by the thousand on the great stretches of shifting white 

 sand. As there is no vegetation whatever at that end of the island, 

 and the prevailing winds, in the opposite direction, makes it impos- 

 sible for them to have been driven there by that agency, it remains 

 an unanswered question how came these myriads of dead and 

 bleached shells in this sand desert? 



At the west end occasional springs of fresh water drip from over- 



