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 %^ (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 

 is most remarkable for 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 inha- 

 bitant 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 pre- 

 served 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 speci- 

 men of this extrordinary species, forms a very ele- 

 gant 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 



