174 BIVALVES. 



of these are remarkably dissimilar in their ap- 

 pearance. 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 wpy (chem6) 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 

 affords 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 in 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 

 a half in breadth. A specimen of this extraox- 

 .dinary species, forms a very elegant baptismal 

 font in the church of St. Sulpice, in Paris, it 

 was presented by the Venetians to Francis I. 

 Large pearls are occasionally found in the 



