63 GENUS VIII, MACTRA. 



Linnseus describes only 8 species, Gmelin has added 19, 



and Dr. Turton none. Total, 27. But it is probable that some 



of the smaller species have inadvertently been placed among 



the TelUncE. 



Lamarck has divided this genvis into two, as follows : 



LuTRARiA. Shell transverse and inequilateral, g-aping at the 

 extremities ; two oblique and diverging centre teeth 

 accompanying a large pit for the cartilage ; no lateral 

 teeth (^Mactra lulraria. See pi. 2. /. 20). 



Mactra. Shell transverse and inequilateral, a little gaping; 

 the hinge tooth folded like a gutter, articulating with that 

 on the opposite valve, and accompanied with a hollow 

 that holds the cartilage ; one or two lateral teeth, com- 

 pressed and inserted (^Mact?a stidtorum. See pi. 2./. 21). 

 Lamarck's genera of Crassatella and Erycina are nearly 



allied to Mactra, both of them having an internal cartilage ; 



but most of the shells placed in these genera are fossil. 



Crassatella. SlicU inequivalve, somewhat transverse, with 

 closed valves, with a lumile sunk deep, and having the 

 cartilage internal ; the hollow for the cartilage placed 

 under the beaks, and above the teeth of the hinge (see 

 Park. Organ. Rem. vol. 3. p. 180. t. 13. f. 2). 



Erycina. An equivalved, inequilateral, transverse bivalve; 

 the hinge teetli two, diverging upwards, with a small 

 intermediate pit ; the lateral teeth compressed and ob- 

 long ; tlie cartilage inserted in the liinge pit (see Park. 

 Organ. Rem. vol. 3. p. 181. t. 13. f. 13). 



