THE ANIMAL LIFE OF THE GROUP. 467 



markets. This knee-cap or umbrella shell is roughly though evenly ribbed 

 without and pearly white within. They attain a diameter of two inches or more 

 and are usually completely covered with a growth of sea-moss. As they 

 are fond of the dash of the spray, they usually cling with great tenacity to 

 the moss-grown rocks along the more exposed portion of the sea-coast. Like 

 their relatives, they feed on algte of various kinds, but are commonly found 

 sticking tight to the rocks, although tliey are known to move about in search 

 of food. 



Experiments have been made on certain European species of limpets for 

 the purpose of showing how difficult they are to di.slodge from their resting 

 places. It was found that it required one thousand nine hundred and eighty- 

 four times the weight of the living animal to detach it from the rocks. 



Chitons. 



The chiton shells "■* are also represented in the sea-shore fauna and, like 

 the members of tlie preceding family, they are found adhering firmly to the 

 rocks. The shell is remarkable in that it is compo.sed of several separate over- 

 lapping plates suggesting a "coat of mail," a name often applied to various 

 species. Specimens may be taken from under stones on the shore at Pearl 

 Harbor and about Hilo, but as there are more than two hundred and fifty 

 living species in the world, more than one of which occurs in Hawaii, the 

 beginner can hardly hope to definitely identify his material. Specimens are 

 of unusual interest, however, as they are believed to be a very primitive type 

 of moUusk and are known to occur elsewliere in very ancient geologic strata. 



One of the prettiest shells to be picked up occasionally on the sea-shore in 

 the islands is the beautifully -banded bubble shell, ^^ the body whorl of which 

 is characteristically marked by two delicate pink bands that are set off from 

 the white ground by well-defined blackish bands. Ajiother .species,"'' with a 

 greenish bod.y, is often found well concealed on mo.ssy rocks along our coasts. 

 The thin pale-green shells are so delicate, however, that they are seldom 

 found except living and attached to the rocks. Although related to the pre- 

 ceding "" family, they are held separate from it as Scaphandridce. 



Sea Slugs. 



The sea slugs,^* and especially the sea hares,'" are curious naked mol- 

 lusks occasionally found cast up on the shore, entangled in the seaweed or else 

 caught in tide-pools along the shore. The ninnerous species vary in size from 

 small animals up to creatures several inches in length. They also vary in 

 form and color to such an extent that they are not easil.v recognized as mem- 

 bers of the great phylum to which the more ordinary sliell-beai-ing animals 

 belong. 



' nydntiua ampbishe. 

 ■ftiata. "^^ Aplysiida 



