1907.] 



STUDIES ON THE LIMPET. 



863 



Table YI. gives ratios for a series of 100 exposed shells from 

 another locality. 



Table VI. 

 Exposed Limpets. 



The numbers measured are rather small to give very definite 

 results ; and the distinction between sheltered and exposed limpets 

 is a little arbitrary. Shells which were attached to the under side 

 of stones, or to the side nearest the shore, or which lurked in 

 nooks and crevices, were taken to be sheltered ; while shells 

 attached to the upper side, or to the side nearest the sea, were 

 considered to be exposed. 



— . — The exposed shells are on the whole narrower than the 

 sheltered shells. 



Ab 



A'r 



-No definite conclusion can be drawn from the differences 



shown by this series. 



™- — Comparison of the ratios for shells below 30 mm. gives 



conflicting results. For shells above 30 mm., however, this ratio 

 is distinctly greater in both sets of exposed shells than in the 

 sheltered set. Exposed shells of 30 mm. and upward are there- 

 fore lower than sheltered shells of corresponding length. 



The fact that the decrease in height becomes apparent only in 

 large shells leads one to think that the decrease is due to the 

 greater erosion to wdiich exposed shells are necessarily subject. 

 The differences between the two sets of shells must be explained 

 as the direct result of the difference in the amount of friction to 

 which they are respectively subjected. 



These observations partly bear out and partly contradict the 

 statement made by Davis and Fleure (5) that the shells of limpets 



