280 MANUAL OF THE MOLLUSCA. 
many tons weight are collected annually near the town of 
Larne alone. (R. 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 
asa basin. (Cuming.) 
The common limpet makes oval 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 
coyered with radiating strie not parallel like those produced by 
their teeth on nullipore. Mr. Gaskoin has a limpet-shell 
encrusted with nullipore, which other limpets haye rasped all 
oyer. In M. D’Orbigny’s collection of Cuban shells there is a 
group of oysters (O. cornucopie), 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 Calyptreide generally, although furnished wita 
lingual teeth (Fig. 96) like those of the animal-feeding Velutina, 
and themselyes manifesting carnivorous propensities (p. 275), it 
is difficult 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 ive. Thus 
the British Nacella pellucida is found on the fronds of the 
tangle, and assumes the form called N. levis, 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” (Cymba, Adams, not Broderip) when it 
roosts on the round stems of sea-weed, and takes the form 
called P. compressa. (Gray.) 
Distribution, 144 species. Britain, Norway, &c. Wellington 
Channel. World-wide. 
Fossil, above 100 species of patellidz, including aemea, L. 
Silurian—. North America, Europe. 
Sub-genera. Nacella, Schum. (= patina, Leach). 
Example, P. pellucida. Pl. XI., Fig. 23. 
Shell thin; apex nearly marginal. 
Animal with the mouth entire below. Branchize not con- 
* A similar circumstance has been noticed in the fresh-water Paludine and Am- 
pullarea, by Dr. Bland and Mr. R. 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 holes in the shell. 
