PLATE LXXIII. 
1. Unio Heyii. (Key's Unio.) Sub-triangular, inflated; posterior side, -with oblique sub-truncation; beak slight; hinge-line 
arcuated; basal line arcuated; umbones prominent, obtuse; surface, with many, concentric wrinkles ; with longitudinal, shallow 
groove from umbones. 
2. U. Blaydsii. ( Blayds* Unio.) Obliquely sub-triangular, inflated; umbones prominent, remote; hinge-line straight; anterior 
side suddenly rounded; posterior side acuminated, with oblique truncation. Length, f in.; breadth, f in. 
3. U. Dawsoni. (Dawson's Unio.) Orbicular; umbones central, large, remote; surface smooth, with a few, faint, concentric 
wrinkles. 
4. U. Amygdala. (Almond Unio.) Inflated; anterior side rounded; posterior side acuminated, with acute termination; um¬ 
bones obtuse, remote; basal line arcuated; surface, with many, acute wrinkles. 
5. U. Rhindii. (Bkind’s Unio.) Sub-acute; basal line arcuated, produced; umbones sub-central, produced, close; hinge-line 
curved; surface, with transverse, shallow wrinkles. 
6. U. Embletoni. (Embleton's Unio.) Sub-triangular ; anterior side short, rounded ; umbones obtuse ; beaks inflected, sharp ; 
hinge-line arcuated; beak sub-truncated, short; surface, with transverse wrinkles. 
7. U. Nanus. (Little-vessel Unio.) Smooth; posterior side elongated, obliquely sub-truncate; sub-acute above; anterior side 
rounded; umbones produced, rounded; hinge-line arcuated. 
8. U. Nucleus. (Kernel Unio.) Inflated, transversely ovate; umbone3 sub-acute, remote; hingo-line straight; anterior side 
acute ; postenor side elongated, acuminate ; basal line arcuated ; surface, with shallow wrinkles. 
9. U. Similis. (Similar Unio.) Compressed; anterior side rounded; umbones hardly produced, contiguous; posterior side 
parallel, obliquely truncate ; hinge-line straight; basal line arcuated; surface, with transverse wrinkles. 
10,11. U. Smithii. (Smith's Unio.) Sub-triangular ; umbones sub-central, prominent, rounded; anterior side rounded; posterior 
side sub-acute ; surface, with transverse, irregular wrinkles. 
12. U. Sub-triangularis. (Sub-triangular Unio.) Sub-triangular, inflated; umbones prominent, remote; hinge-line parallel; 
basal line undulated; surface smooth, with slight elevation towards umbones. 
13. U. Dubius. (Doubtful Unio.) Sub-ovate ; both sides rounded; umbones produced, rounded ; hinge and basal lines arcuated; 
surface, with concentric wrinkles. 
14,15. U. RugOSUS. (Rugged Unio.) Sub-triangular, ventricose; umbones prominent, remote ; anterior side rounded; ligament 
produced; surface, with unequal, concentric wrinkles. Length, 2 J in.; breadth, 3£ in.; thickness, 2^ in. 
16, 17. U. Turgidus. (Turgid Unio.) Inflated ; umbones prominent; anterior side short, sub-truncate; posterior side parallel, 
truncated below; hinge-line parallel; basal line, with small flexure ; surface, with strongish wrinkles. Thickness, f in.; breadth, 
in- 
18. U. Aldamii. (Aldam's Unio.) Sub-compressed, flexuose, sub-triangular; umbones sub-central, obtuse; hinge-line arcuated; 
anterior side, with flexure below ; posterior side rounded, with shallow sulcus from umbones ; basal line flexuose. Length, If in.; 
breadth, 2f in.; thickness, 1 in. 
19. U. Pyramidalus. (Pyramidal Unio.) Sub-triangular, cuneiform, pyramidal; umbones large, obtuse; anterior side short; 
posterior side elongated; base acute, flexuose; surface, with shallow wrinkles. 
20. U. Agrestis. (Rustic Unio.) Sub-compressed; transversely elongated; anterior side rounded; posterior side lengthened, 
sub-acute; umbones obtuse, remote; on posterior side a longitudinal, oblique, shallow groove, below which is a flexure; surface, 
with coarse, transverse wrinkles. Thickness, f in. 
21. U. Transversus. (Transverse Unio.) Transversely elongated; umbone3 blunt, obliquely rounded; anterior side short, 
rounded; posterior side long, truncate; hinge-line straight; basal line, with slight flexure ; surface smooth. 
22. U. SubPOtundus. ( Sub-rotund Unio.) Sub-rotund; umbones sub-central, produced, blunt, remote; hinge-line arcuated; 
surface, with acute, concentric wrinkles . 
23,24. U. Gerardi. (Gerard’s Unio.) Transversely ovate, inflated; umbones produced, rounded, contiguous; posterior side 
short, truncated; anterior side long, sub-truncated ; hinge-line parallel; external surface, with a few, concentric wrinkles. 
25. U. Exoletus. (Worn Unio.) Transverselyeiongated; surface smooth; umbones blunt; anterior side round; posterior side 
acuminated, sub-acute ; hinge-line arcuated; basal line parallel. 
26. U. Lateralis. (Broad Unio.) Transversely elongated, sub-quadrate, cuneiform; sides unequal; umbones produced, with 
acute beaks. Length, i in.; breadth, l£ in. 
27. U. Bipennis. (Two-winged Unio.) Transversely elongated, hatchet-shaped; sides unequal; umbones produced, remote, 
hinge and basal lines parallel; anterior side short, rounded; posterior side elongated, sub-truncate from hinge-line; surface 
smoothish, with a few, trausverse grooves. 
28,29. U. Sulcatus. (Furrowed Unio.) Sub-triangular, compressed; umbones prominent, close, reflected, sub-acute; surface 
smooth, with concentric sulci; posterior side arcuated ; anterior side rounded ; basal line parallel. Length, \\ in.; thickness, ^ in. 
30. U. Levedensis. (Goarse Unio.) Sub-triangular, cuneiform; umbones rounded; anterior side short; posterior side long, 
acuminated, truncated; basal margin straight; surface, with transverse wrinkles. 
31. U. Senex. (Old Unio.) Transversely elongated, sub-compressed; umbones obtuse, remote; anterior side short; posteiioi 
side long, sub-truncated; hinge-line arcuated; with deepish, transverse sulcus; basal margin, with slight hollow; surface, vri 1 
transverse wrinkles, and a few, longitudinal sulci. Length, f- in. , 
32,33. U. Polmontensis. (Polmont Unio.) Oblong; umbones central, arcuate, remote; hinge-line straight; surface smoo 
with a few, transverse sulci. 
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