xii. CONCHYUA-DITHYRA. 



44. MoDiOLA. — Testa suhlongitudinalis, umhonibus Siihtermina- 

 libus. 



Shell somewhat longitudinal, with the beaks 

 nearly terminal. 



49 Pinna. — Testa cuneiformis, apice dilatato hiante. 



Shell wedge-form, dilated and open at the top. 



47. Lima. — Testa basi auriculatci. 



Shell with auricles at the base. 



** Cardo dentibus primariis, laleralibus nullis. 

 Hinge with primary teeth, but no lateral ones. 



25. SoLEN. — Testa transversim linearis, cardine subtenninali. 

 Shell transversely linear, with the hinge near 

 the end. 



43 Mytilus. — Testa longitudinalis, umbonibus terminalihus 

 rectis. 



Shell longitudinal, with the beaks terminal and 

 straight. 



3. Gastroch^na. — Testa hiantissima, dentibus obsoletis trans- 

 versim lamellosis. 



Sliell very open, with the teeth obscure and 

 transversely laminar. 



48. AvicuLA. — Testa basi transversim caudala. 



Shell with a transverse projection at the base. 



