The Limpets. Tent Shells 



feed upon minute vegetation that grows on them in patches. A 

 pecuHar noise is made by the scraping of the rock surface by the 

 radulas of ^ many feeding Hmpets. At rest this remarkable toothed 

 tongue is coiled like a watch spring. Still louder is the rasping 

 sound of limpets dragging their shells over wet barnacle-covered 

 rocks, between tides. 



Instead of having true gills, like those of its near relatives, 

 this limpet has these reduced to mere stumps, and replaced by 

 a series of gill plates, encircling the mantle. With these breathing 

 organs the moUusks are able to remain for hours out of sea water, 

 and to be exposed to rain without inconvenience. The oyster 

 catcher deftly pries their shells from the rock with its case knife 

 bill. 



We shall find limpets of this genus in collections but not 

 on our seashores. They have a wide distribution in the eastern 

 and southern hemispheres. 



The Common Tent Shell or Limpet (P. vulgata, Linn.), 

 found from the Arctic shores to Spain, is a solid, conical shell, 

 its peak a little in front of the centre. Ribs radiate from apex 

 to margin; small ribs, and still smaller stria, lie between the 

 cardinal ones. Colour varies from grayish brown to yellowish. 

 All are streaked or mottled, and become worn or overgrown 

 with nullipores when old. The linings of the shells are polished 

 and often opalescent, sometimes brighter in colouring than the 

 exterior. Length, i to 2 inches. 



Habitat. — Europe. 



The Rusty Limpet (P. ferruginea, Gmel.) is very heavy, and 

 deeply sculptured into rounded pillars or ridges that radiate from 

 the apex, and make the margin deeply notched. Concentric 

 striae cross these ridges. The back is rusty brown, shaded with 

 white in wavy lines. The lining is white porcelain. Length, 2 

 to 4 inches. 



Habitat. — ^Mediterranean. 



The finest specimens of tent shells are found in far off tropical 

 regions. P. longicosta from the Cape of Good Hope, has the 

 ridges of its heavy shell prolonged into thin blades. P. granu- 

 lans has its peaked roof beset with stout prickles. The flat 

 yellow back of P. aspera of Madeira bears a set of radiating saw- 

 toothed ridges as sharp as knife blades. P. radians from New 

 Zealand has a flattened, almost smooth, finely mottled exterior 



235 



