PLATE LXX. 
1. Pinna Arcuata. {Arcuated Pinna.) Short, equilateral, arcuated, ventricose ; beaks obtuse, 
curved; hinge-line bent; anterior half with wide, longitudinal stride and shallow sulci; opposite side 
smooth, with some transverse lines of growth. 
2. P. Folium. * ( Leaf Pinna.) Elongated, curved, sub-quadrate ; one side, with oblique, trans¬ 
verse folds ; the other with curved, shallow folds. 
3. P. Tetragona. {Tetragonal Pinna.) Abruptly conical, arcuated, smooth; with obscure, 
longitudinal ribs, with a suture in centre. 
4. P. Mitis. {Buried Pinna.) Elongated, straight; beaks acute; surface, with concentric 
ridges. 
5. P. Granulata. {Granulated Pinna.) Broad, conical, equilateral, convex; anterior side 
rounded; edge thick towards anterior side; surface obscurely decussated. Length, 8 in.; breadth, 
6 in. 
6. P. Afiinis. {Allied Pinna.) Equilateral, ventricose, straight, wedge-shaped, smooth; with 
irregular, longitudinal ribs, disappearing near the edge. 
( 87 ) 
