170 BIVALVES. 



OBSERVATIONS ON THE SHELL AND ITS 

 INHABITANT. 



This genus, as it stands in the Linnaean clas- 

 sification, contains only twenty-six species, but 

 some of these are remarkably dissimilar in their 

 appearance. It includes regular and irregular, 

 equivalve and inequivalve shells, also some that 

 are attached to marine substances, and others 

 that are free. The callous ridge at the hinge is 

 the most decided character of the genus. The 

 name is derived from x*^ (cheme) a gaping, 

 and is applicable to many of the species ; it is 

 probable that all those which have an opening at 

 the margin, possess a byssus, by which they are 

 fastened to rugged substances. This genus af- 

 fords subject of amazement in the uncommon 

 size to which some of its species attain. The 

 Giant Clam (Chama Gigas) is a specimen of 

 unusual magnitude in a shell : it is indeed the 

 largest of all testaceous productions. One of 

 these shells described by Linnaeus, weighed four 

 hundred and ninety-eight pounds ; and he says 

 that its inhabitant furnished one hundred and 

 twenty men with a day's food. So great were 

 the weight of the shell and the strength of the 

 muscles, that by suddenly closing its valves, it 

 cut asunder a cable ; another specimen brought 

 from Sumatra, is preserved at Arno's Vale, in 

 Ireland, its weight is five hundred and seven 

 pounds ; the largest valve measured four feet 

 six inches in length, and two feet five inches and 



