2. Anodon. Hinge without teeth, but furnished 

 with a transverse elongated lamina. 



T2/pe. Mytilus anatinus, Montagu. 



3. Unio. Hinge with a single obtuse jagged tooth, 

 which is two-lobed in one of the valves ; transverse 

 laminae none. 



Type. Mya margaritifera, Montagu. 



4. Mysca. Hinge with a transverse crenate tooth, 

 which in one valve is two-lobed ; and a transverse 

 elongated lamina, which is double in one of the 

 valves. 



Tijpe. Mya ovalis, Montagu. 



