44 Dwellers of the Sea and Shore 



scallop, the oyster, and other well-known edible shell- 

 fish. Beside the name Pelecypoda, meaning "hatchet- 

 shaped" foot, and which, by the way, is in many 

 instances a misnomer, the term Acephala is used, indi- 

 cating "without a head." Another name, Lamellihran- 

 chiata, in reference to the type of gills peculiar to these 

 animals, has also been employed. But the terminology 

 of science contains no name more descriptive or correct 

 than the easily remembered, easily pronounced, and 

 easily understood popular name "bivalve." Fjr every 

 animal in this class has two valves (the word "valve" 

 meaning "shell"). 



Bivalve mollusks, unlike their univalve brethren, do 

 not build egg cases. They do, however, lay eggs. 

 These, as a rule, are not kept within the shell among the 

 fleshy folds, and when they hatch they give rise to free- 

 swimming young somewhat similar to those of the 

 moon snail. The fate of the majority is likewise sim- 

 ilar. It has been asserted by naturalists that probably 

 not more than one in a million reaches maturity. 



On the whole, the bivalves have acquired a more 

 stationary habit of living than the univalves, but there 

 are individuals among the former which can travel with 

 remarkable rapidity. In speed and action the fastest 

 univalve cannot match them. The scallop [Pecten) is 

 one case in point. It adopts the singular method of 

 quickly opening and closing its valves; thus propelling 

 itself through the water in a jerky, butterfly sort of 

 flight. The extreme case, though, is to be seen in the 

 razor clam {Solen ensis). The characteristic "razor 

 shell" of this odd-looking mollusk is familiar to every 

 one who has visited a sandy beach. They are easily to 



