36 CONCHOLOGY. 



M. gigantea. The gigantic Mactra. 

 Species in which the cardinal teeth are ahuost obsolete, 

 in consequence of the enlargement of the pit of the ligament. 



M. stultorum. The fool's Mactra. PL 9, fig. 6. 

 Species in which all the teeth are very large, lamellous, 

 striated longitudinally ; colour reddish brown. 



M. solida. The solid Mactra. 



Species thick, solid, without epidermis ; lateral teeth finely 

 striated. 



M. trigonella. The three-cornered Mactra. 

 Species in which the lateral teeth are almost obsolete ; 

 exterior surface smooth. 



M. triangularis. The triangular Mactra. 

 Species very small, strong, opaque, white ; inside white ; 

 margin strongly crenated. 



M. crassa. The thick Mactra. 



Species very thick, solid, striated longitudinally ; the car- 

 dinal teeth obsolete, or almost so ; the lateral very thick, 

 very close, and reflected ; an external ligament as well as an 

 internal one. 



3. Crassatella. Eleven species. 



May be easily known from the Mactra and Lutraria, as 

 the valves, when closed, fit exactly, and do not gape. It is 

 remarkable that all the living species contained in this genus 

 only exist in the seas of Australasia, while at least seven 

 species in a fossil state are found in France. 



Shell inequilateral, sub-orbicular, close, equivalve, some- 

 times attenuated at one end ; two divergent primary teeth, 

 with a cavity at the side ; lateral teeth obsolete : ligament 

 internal, inserted in the cavity of the hinge. 



Crassatella Kingicola. Crassatella subradiata. 



C. donacina. C. contraria. 



C. sulcata. C. cuneata. 



