THE ANIMAL LIFE OF THE GROUP. 443 



foot, and is an allusion to the fact that the entire lower portion of the body is 

 thickened and flattened to form a broad muscular foot adapted to their cling- 

 ing and crawling habits. In the common and more typical forms, the aper- 

 ture, which is the opening into the spiral shell, is closed when the animal is 

 retracted, by a small horny or shelly plate called the operculum, but both the 

 spiral shells and the operculum are absent in certain gasteropods. 



The third division - includes such creatures as the mussels, clams, scallops 

 and oysters, in which a right and left valve or shell can be plainly recog- 

 nized. For this reason they are commonly spoken of as bivalves. The living 

 animal has broad, flat gills on each side of the body to which water is brought 

 through a tube called the siphon. The food, consisting of minute plants and 

 animals, is strained out of the water as it passes through the incurrent and excur- 

 rent tube. The bulk of the soft part of the animal is called the foot and is 

 suited for digging. 



]Ml>;sel!-;, Clams, Scallops and Oysters. 



While there are a number of species of bivalves in the waters about the 

 islands, j^erhaps not more than fifteen or twenty species are common on Oahu. 

 Of these the one mo.st frequently met with is the common mussel,^ which in 

 many places, as at Diamond Head and Pearl Harbor, almost pave the shore 

 below the low-tide mark. They are from an inch to two inches in length ; the 

 right and left valves are equal, slightly ridged, and are covered with an epi- 

 dermis which varies from black to light yellow. The hinge has minute 

 teeth, and the beak is at one end of the hinge-line. They live attached to 

 rocks, shells, piles or other objects by a number of threads called the 

 byssus. A species occurring in Europe is much esteemed as food. The Ha- 

 waiians use the nahawele, as they are called, but so far as the writer knows they 

 have never been gathered for market. 



A method formerly employed by the natives in preparing this common 

 mollusk for food should be of interest to sea-shore campers. A spot was found 

 where the mussels were exposed at low tide, and over the bed of shells, drift- 

 wood was piled and a fire lighted. The heat caused the shells to open and at 

 the same time roasted the fleshy part within, rendering it very palatable. The 

 natives also gathered them from the shallow water and placed them in wooden 

 calabashes in which water was heated by means of hot stones. In a few min- 

 utes the animal would be thoroughly cooked. The water was then drained off 

 and a pinch of sea salt added to bring out the flavor of the food. 



The ilytihis. or edible mussel, is readily separated from the two or three 

 common .species of Perna, especiall.v a small black form* which it somewhat 

 resembles, by the more compressed form of the shell and by the several tooth- 

 like notches along the straight hinge-line. The Perna are further marked by 

 conspicuous flaky lines of growth which are important characters in tlie 

 various common forms. One species, the papaua of the natives, common at 



" Pehrijpuda or LameUibraiirhiala. " ili/tihiii ••rebristrintiit:. ' ilellnn = (Ptihi) ctMUirnU-n. 



