GASTROPODA. 25 



resemble in external shape ordinary Limpets, but are perforated at 

 or near the apex, or more or less slit at the front margin. The 

 hole or slit gives passage to a tubular fold of the mantle, through 

 which the water apparently flows to the gills. The largest species 

 are from California and South America, and others are found, but 

 not abundantly, on most shores. The animal of the large Luatpina 

 crenulata from California is eight or ten inches in length, and 

 almost conceals the shell, and the shell of the South-African 

 Pupillcea aperta is also all but hidden beneath the mantle of the 

 animal. 



The Acmceidce are called false Limpets, because, although the [Case 11, 

 shells are identical with the true Limpets, the animals differ by K_a -J 

 having only a small gill on the left side of the neck, whilst the 

 Patellce have the gills greatly developed all round the sides of the rp 

 foot. Both the true and the false Limpets are littoral and found 11g-12a.] 

 on rocks between tide-marks. They have the power of excavating 

 the surface to which they attach themselves, and adhere so firmly 

 that it is easier to break the shell than detach the animal. The 

 largest-known Limpet (Patella mexicana) inhabits the west coast 

 of Central America, its shell having sometimes a diameter of 1 2 

 inches. The Limpets are vegetable-feeders and fond of seaweeds of 

 various kinds, which they rasp with their remarkable spiny tongues. 

 That of the common English Limpet (P. vulgata, fig. 12) is longer 

 than the shell itself, and armed with as many as 1920 glassy hooks 

 in 160 rows of twelve teeth each. The Limpet is commonly used 

 for bait in the sea-fishing off the Scottish coast, and vast quantities 

 are consumed as food in some parts of Ireland. Some Limpets, 

 such as P. compressa, P. mytilina, &c, are found on the stems of 

 floating seaweeds, and have the shells usually thinner and smoother 

 than the Rock-Limpets, which have to resist the fury of the 

 breaking waves. 



The " Coat-of-mail shells/' or " Sca-woodlicc " (Chitonida) , [Case 12 

 have their back armed with eight shelly plates which overlap one B-I), l 

 another like tiles, and, like woodlice, have the power of rolling 

 themselves into a ball. These plates are imbedded at the sides 

 into the fleshy mantle, beneath which, on each side of the foot, are 

 arranged the gills. A Chiton differs in many respects from other 

 Mollusca. It has a shell like an Isopod Crustacean, a heart down 



