OF CONCHOLOGY. 51 



been found, sparingly, 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 £enus 

 have only been found to inhabit the 

 ocean. These shells lurk in the sand 



