PLATE LXXX. 
1. Cardium Gentianum. {Gent's Cardium.) Cordiform; valves equal, compi'essed, longitudi¬ 
nally sub-carinated; beaks incurved; surface, with many, longitudinal, tuberculated ribs. 
2, 3. Isocardia Minima. {Very small Isocardia.) Sub-deltoidal, globose; anterior side trun¬ 
cated ; posterior side flattened, cordiform. 
4. I. Striata. {Striated Isocardia.) Rectangular, inflated; anterior side rounded ; surface, 
with curvilinear striae. 
5. I. Cor. {Heart Isocardia.) Cordiform, inflated; with strong, transverse wrinkles; beaks 
curved, acute. 
6. I. Axiniformis. {Axinus-formed Isocardia.) Transversely elongated, cuneiform; beaks 
short, involute; surface glabrous, with many, concentric striae. 
7. I. Abrupta. {Abrupt Isocardia.) Triangular, inflated; anterior side straight; beaks pro¬ 
duced ; surface, with oblique striae; anterior side with longitudinal striae; front, with five or six, 
longitudinal ridges. 
8. 9. Pholadomya Margaritacea. {Pearly Pholadomya.) Transversely ovate; anterior side 
produced, with longitudinal keel and several ridges; beaks prominent, incurved. 
10. Sphsera Corrugata. {Corrugated Sphcera.) Gribbose, ponderous ; surface, with coarse 
corrugations; rugae, transverse, obtuse. 
11. I. Triangularis. {Triangular Isocardia.) Triangular, smooth, inflated; beaks small, 
inflected; surface, with strong, concentric lines of growth and fine, longitudinal striae; basal line 
arcuated. 
12. I. Similis. {Similar Isocardia.) Yentricose, transversely oblong ; centre of disc flattened ; 
anterior side small; base straight; surface, with transverse undulations. 
13. 14. Opis Similis. {Similar Opis.) Gibbose, rhomboidal; anterior side, separated by 
serrated keel; lunette cordiform, flat; beaks involute ; surface transversely ribbed. 
15, 16. Opis Lunulata. {Luniform Opis.) Rhomboidal, inflated, separated by projecting keel; 
beaks involute, produced; posterior side rounded, with incurved margin, confining deep lunette; 
beaks involute; anterior side, with series of steps ; right valve, with two teeth, some in left; surface, 
with transverse ribs; base acute. 
17. I. Nitida. {Shining Isocardia.) Cordiform; beaks involute ; surface smooth, shining.- 
( on ) 
