GO^CRYLl A— DITHYRA. 23. 67 



23. MACTTIX—LINNE. 



Testa subtrigona, cequivalvis, lateribus subhiantibus. Cardo dente coch- 

 leariformi, cum dente trigono adjecto : lateralibus laminatis, valves 

 alterius didymis. Ligamentum internum. 



Shell somewhat "triangular, equivalve, a little open at the sides. 

 Hinge with a spoon-shaped tooth and an adjacent triangular one : 

 the lateral teeth laminar, double in one of the valves. Ligament 

 internal. 



The shells confined to the above generic character form a very 

 natural family, remarkable for the number strength and position of 

 the teeth. In one valve there is a single elongated lateral plate on 

 each side, which closes between two in the other. And in this res- 

 pect they resemble the fresh-water shells of the genus Mysca, but 

 the primary teeth are very different, and the ligament is internal. 



Those of the first division, or such as have the lateral teeth striate 

 in a direction ojiposite to their transverse e.xtension, are usually 

 thick and solid : and such as have the lateral teeth quite plain, are 

 thin and semitransparent. 



They inhabit the sandy parts of our coasts. 



* Denies later ales striati. 1-5. 

 The lateral teeth striate. 



Mactea testa, ovato-trigond Ueviusculd mquilaterali, lateribus obliquis, solida. 



umbonibus incurvis. 

 Shell oval-triangular nearly smooth and equilateral, with the sides 



oblique, and the beaks incurved. 



K 2 



