PLATE LXXIX. 
1. Axinus Rotundatus. ( Rounded Axinus.) Orbicular; umbones central, acute, remote; 
surface smooth. Length, in. ; breadth, \ in. 
2, 3. A. Minimus. ( Least Axinus.) Orbicular, transverse ; beaks central, large, produced; 
hinge-line straight; surface smooth. Width, £ in. 
4. A. Latus. ( Broad Axinus.) Transversely elongated ; beaks blunt ; anterior side short, 
rounded; basal line slightly curved ; surface smooth. 
5, 6, 7. A. Obscurus. (Obscure Axinus.) Sub-triangular, transverse ; beaks obtuse, central; 
posterior side cuneiform, attenuated below to obtuse point ; base curved ; surface smooth. Fig. 7, 
young state. 
8. A. Dubius. (Doubtful Axinus.) Transversely elongated; curved; anterior side short, 
narrowed; basal line arcuated. 
9. A. UndatUS. (Waved Axinus.) Sub-triangnlar, smooth, inflated; umbones small, obtuse; 
sides equal; posterior side acute, with triangular flexure from centre of valve to basal margin. 
Length, f in. ; breadth, % in. 
10. 11. A. Pusillus. (Slender Axinus.) Triangular, smooth; beaks prominent, central. 
Length and breadth, ^ in. 
12. A. Parvus. (Small- Axinus.) Smooth, sub-triangular, inflated ; umbones prominent, 
inflated, close; posterior side acute, elongated. Length, £ in. ; breadth, in. 
13, 14. Megalodon CueullatUS. (Hooded Megalodon.) Oblong, smooth, convex, thick, 
ponderous ; beaks pointed, incurved ; with deep pit for anterior muscle, close to thick plate for 
hinge-teeth. 
15. Isocardia Tumida. (Tumid Isocardia.) Cordiform, inflated, elongated ; beaks tumid, 
involute ; surface, with transverse lines of growth, crossed by longitudinal sulci. 
16. I. Rhomboidalis. (Bhomboidal Isocardia.) Rhomboidal; anterior side depressed ; smooth; 
posterior side, with many, concentric sulci ; basal line triangular. 
17. A. Angulatus. (Angular Axinus.) Sub-triangular, convex, oblique ; anterior side short, 
curved ; posterior side cuneiform, with ridge from beaks, producing angle on both sides ; surface flat, 
with a few lines of growth ; lunette ovate, curved. 
18. 19. I. Rostrata. (Beaked Isocardia.) Ventricose, deltoidal; anterior side produced, acute; 
posterior side depressed, rounded; beaks short. 
20,21. Hippopodium Ponderosum. (Ponderous Hippopodium.) Gibbose, rugged, ponderous ; 
anterior lobe angular, acute; posterior lobe smaller, forming boundary of cordiform pit, which is 
deep and extends to hinge-tooth, with well-marked lines of growth ; in shape like horse’s foot. 
22, 23. I. Sulcata. (Furrowed Isocardia.) Orbicular ; beaks remote, incurved, with cordiform 
impression beneath ; surface pearlaceous, with many, longitudinal sulci. 
24, 25. I. Angulata. (Angulated Isocardia.) Sub-triangular ; beaks obtuse, large ; surface 
smooth ; base curved, acute at both ends. 
26,27. I. Tener. (Tender Isocardia.) Obovate: anteriorly sub-truncated; beaks produced; 
surface smooth ; anterior side circumscribed with slight ridge; shell thin. 
28, 29. I. Concentrica. (Concentric Isocardia.) Oval, cordiform, transversely elongated; 
beaks projecting, incurved ; surface smooth, with many, transverse sulci ; shell thin. 
30, 31. Cardiomorpha Oblonga. (Oblong Cardiomorpha.) Oblong, sub-compressed, very 
short; beaks incurved; posterior side large ; hinge-line straight ; surface smooth. 
( 98 ) 
