OF CONCHOLOGY. 51 



been found, sparino^ly, at the mouth 

 of the Tees in Yorkshire. Cockles, 

 in general, live just under the surface 

 of the sand, barely' covered ; they are 

 necessitated to be near the surface, 

 from the shortness of their tube, by 

 which they draw in and throw out the 

 water. 



The French have divided the Car- 

 dium into three genera: Cardium, 

 Bucarde, and Cordiformes. 



In Turton's Linne fifty-two species 

 are described ; fifteen species have 

 been found in Great Britain. 



Genus 8th.-— MACTRA. Animal 

 a Tethys ; shell bivalve, with unequal 

 sides, equivalve ; middle tooth of the 

 hinge complicated, with a small hol- 

 low on each side, lateral teeth, remote, 

 and inserted into each other. Linn. 

 Syst. 307. Plate 6th, fig. 8th. 



Habitation, Shells of this cfenus 

 have only been found to inhabit the 

 ocean. These shell's lurk in the sand 



