41 

 MYA. 



GENERIC CHARACTER. 



Shell elongated, nearly equivalvCj gaping at both 

 endsj but in a greater degree at the posterior end ; hinge 

 with a single large, compressed, dilated tooth, pro- 

 jecting vertically in one valve ; the other valve with- 

 out any teeth ; muscular impressions two, lateral, 

 distant ; anterior one rather narrow ; posterior one 

 nearly orbicular ; palleal impression with a large 

 sinus. 



OBSERVATIONS. 



This genus is allied to Jlnatina, Lam., Lutraria, 

 Lam. and Sphenia^ of Tiirton, which last has been 

 united with My a by G. B. Sowerby. The recent 

 species are few in number, and as Mr. Sowerby ob- 

 serves, " all belonging as far as we know to the 

 northern hemisphere.'^ One species only inhabits 

 the coast of the United States, the M. arenaria, Lin., 

 which also occurs among the fossils of the Newer 

 Pliocene, in Maryland, but no other species has 

 hitherto been observed in the United States. La- 

 marck describes only four recent species. Deshayes 

 enumerates five in the Tertiary beds. 



