232 PATELLIDiE. 



gata were so deep^ tliat little more than the crown of 

 the shell was visible outside. On the Dorsetshire coast 

 the chalk-rocks are also excavated in the same manner, 

 but not so deeply. Specimens are not unfrequently 

 found on impui'e limestone^ which are constricted or 

 indented at the edges, in consequence of the excavation 

 having been hindered by the greater hardness of one 

 side of the spot occupied by these limpets. The animal 

 feeds on small delicate sea-weeds of a foliaceous kind, as 

 well as on Melobesia polymorpha, that encrust the rocks 

 at low water, by means of its long tongue, which is coiled 

 spirally, like the mainspring of a watch set round with 

 spring- cogs. This instrument is thrust out fi'om side 

 to side ; and when charged with food, it is withdrawn 

 into the stomach, unloaded, and again put forth. The 

 mark left on the face of a rock, coated with a film of 

 the fine sea-weed mentioned above, by a limpet after 

 grazing resembles the track of a sea-worm : indeed a 

 late eminent geologist had a large slab thus marked cut 

 out of the rock, and sent to him with great care, in 

 order to publish the supposed discovery of a new Anne- 

 lidan ichnolite in the old red sandstone; fortunately 

 the mistake was pointed out to him before proceeding 

 further. Each limpet appears to have its own feeding- 

 ground or pasturage ; its tracks are sometimes numerous, 

 and deviate in different dii^ections. [Mr. Peach has 

 ascertained that it does not retire in the winter to deeper 

 water on the coast of Caithness, and that it always 

 returns home before the ebbing tide leaves it dry. Its 

 firm adhesion to the rock is extraordinary. In order to 

 test the strength of its tenacity, Reaumur suspended a 

 weight of from 28 to 30 lbs. from the shell of a limpet 

 attached to a stone ; this weight it sustained for some 

 seconds : less weights failed to overcome its resist- 



