45 



MACTRA. 



MACTRA SOLI DA. — LifiTUeUS. 



Lister, <.25S,/. 87. 

 The Mactrae, separated from the Lutrariae, now con- 

 stitute a numerous and well defined genus. They are 

 marine shells, some of a large size, almost always sub- 

 triangular, slightly gaping at the sides, either smooth 

 on the exterior or transversely ribbed. The charac- 

 ter of the hinge is very singular; on each valve, be- 

 neath the apex, is a compressed tooth, bent or angu- 

 lar, like two divergent pieces, at the side of which is 

 a subcordiform oblique cavity, to which the ligament 

 is attached. There are also two lateral teeth, com- 

 pressed and inserted, one of them more or less near 

 the cavity of the ligament, and the other near to the 

 primary tooth. In some species, where the cavity of the 

 hinge is very large, the primary tooth is oblique, and al- 

 most obsolete ; but the lateral teeth always exist. 

 Mactra gigantea Mactra Helvacea 



Spengleri grandis 



striatella stultorum 



carinata maculosa 



