280 MANUAL OF THE MOLLTJSCA. 



many tons weight are collected annnally near the town of 

 Larne alone. (E. Patterson.) 



On the western coast of South America there is a limpet 

 which attains the diameter of a foot, and is used by the natives 

 as a basin. (Cuming.) 



The common limpet makes oyal pits in timber as well as in 

 chalk. Small individuals sometimes roost habitually on larger 

 specimens, and make an oval furrow on the shell. The surface 

 on which limpets roost, and some space around it, is often 

 covered with radiating striae not parallel like those produced hy 

 their teeth on nullipore. Mr. Gaskoin has a limpet-shell 

 encrusted with nullipore, which other limpets have rasped all 

 over. In M. D'Orbigny's collection of Cuban shells there is a 

 group of oysters (0. cornucopict) , with a colony of the Hipponyx 

 mitrula sheltered in their interstices ; these limpets have not 

 only fed on the nullipore with which the oysters are encrusted, 

 but have extensively eroded the epidermal layer of shell 

 beneath.* 



As to the Calyptrceidce generally, although furnished witn 

 lingual teeth (Fig. 96) like those of the animal-feeding Velutina, 

 and themselves manifesting carnivorous propensities (p. 275), it 

 is diflB.cult to understand how they can travel in quest of food. 



The shape of some species of limpet is believed to vary with 

 the nature of the surface on which they habitually live. Thus 

 the British Nacella pellucida is found on the fronds of the 

 tangle, and assumes the form called N. Icevis, when in lives on 

 their stalks. (Forbes.) The Acmcea testudinalis becomes 

 laterally compressed and is called A. alvea when it grows on the 

 blades of the Zostera (Gould) ; and Patella miniata of the Cape 

 becomes a new " genus " {Cymha, Adams, not Broderip) when it 

 roosts on the round stems of sea-weed, and takes the form 

 cqUgUl P. compressa. (Gray.) 



Distrihution, 144 species. Britain, Norway, &c. "Wellington 

 Channel. "World-wide. 



Fossil, above 100 species of patellidse, including acmcea, L. 

 Silurian — . North America, Europe. 



Suh-genera. Nacella, Schum. (= patina, Leach). 



Example, P. pellucida. PL XL, Fig. 23. 



Shell thin ; apex nearly marginal. 



Animal with the mouth entire below. Branchiae not con- 



* A similar circnmstancc has been noticed in the fresh-water Paludince and Am- 

 pullaria, by Dr. Bland and Mr. B. Swift ; in the absence of other food they devour the 

 green vegetable matter incrusting one another's shells, and in doing this remove the 

 epidermis, or even make lioles in the shell. 



