

PATELLA. 1 1)7 



deepest. Probably the excavation results from the 

 mechanical action of the foot surface and of the bevelled 

 edge of the shell. During life the animal constantly 

 leaves and returns to its home, and even the comparatively 

 soft foot must, therefore, bring about an appreciable 

 amount of wear, especially as fixation is usually preceded 

 by a certain amount of shuffling or twisting round on the 

 scar. The deeper margin of the scar clearly indicates 

 shell action. 



An allied form, lielcion pellucidum, found at the top of 

 the Laminarian zone, lives, when adult, in a sheltered 

 " home " excavated in the bulb or, more rarely, in the 

 frond of Laminaria, and possesses the same faculty of 

 returning thereto after excursions. The depressions in 

 the Laminaria surface are deeply eaten out, and have 

 tracks leading from them. The shell is thinner than 

 that of Patella. 



Food and Exemies. — The chief food of limpets consists 

 of the minute Algae covering the rocks, but they also eat 

 the larger forms Corallina, Melobesia, Fucus, and Lamin- 

 aria. With this food they must also take in a number of 

 minute animals. The details of the feeding process are 

 discussed later, in the description of the alimentary canal. 

 They feed, at least partly, while the tide is low, returning 

 to their scars with its advance to avoid danger from the 

 tidal wash, but it seems likely that they also feed a good 

 deal when covered by water; some, indeed, have actually 

 been watched doing so, and, moreover, the finest limpets 

 are often found low down on the shore where their 

 uncovered period is necessarily very limited. Aquarium 

 specimens also can be kept submerged for weeks, 

 apparently without ill effect. On the other hand, tiny lim- 

 pets and feeble scars occur in abundance high up the shore. 

 The rock barnacles (Balanus) compete with the limpets for 



