86 THE NAUTILUS. 



great strength of shell shows how well they are protected to with- 

 stand the surf of the exposed heach. 



On such a beach Strombus pugilis is the most common visible 

 Gasteropod in the winter. Others may be abundant at other seasons 

 of the year. I found none alive nor did I find a dead shell within 

 the still waters of Clearwater Harbor, although the flats and bottom 

 were composed of sand as is the outside beach ; and a series of ex- 

 tremely low tides allowed me to traverse miles of bottom not ordi- 

 narily exposed at low tide. Since they are cast up by the surf in 

 large numbers in a storm they must be abundant just beyond the 

 breaker line. 



Within the mantle cavity I found a species of oyster crab that 

 Miss Rathbun has given the name of Pinnotheres strombi. A com- 

 mensal of this sort I believe is unique in a Gasteropod shell. 



Every collection of tropical marine shells contains the shells of 

 Strombus. The bright colors exhibited by most of the species are 

 perhaps its chief attraction. Its activity when alive is noted all 

 through the literature. Not alone are its movements described but 

 pages are covered with beautiful colored drawings of the animal. 

 Most of the activities have been described from animals under ab- 

 normal conditions, and the drawings made from animals out of the 

 water. Nowhere can I find a sketch nor a description of the animal 

 in a living attitude. 



Locomotion in Strombus and its allies is peculiar. This is due to 

 the structure of the foot. The operculum has changed from an 

 organ of protection to one of locomotion. Situated as in most Gas- 

 terpods on the dorsal surface of the metapodium, it is peculiar be- 

 cause it is joined to the foot by about one-third of its surface. The 

 two-thirds free extends downward and in a posterior direction, with 

 its slender point turned toward the left side. The propodium and 

 mesopodium compose one-sixth the ventral surface of the foot, the 

 rest is metapodium. 



I quote from the voyage of the " Astrolabe :" " Le form particu- 

 lier de leur pied ne permet pas de marcher comme les Gasteropodes. 

 Ne pouvent pas ramper ils sautent en prenant un point fixe sur le sol 

 a l'aide de leur opercule." Adams in the voyage of the " Samar- 

 ang " describes their method of locomotion as rolling over and over. 

 Both of these observations are founded on fact ; the former was ob- 

 served in the water and the latter on land. 



