PLATE LY. 
1, 10. Leptsena Aurita. {Eared Leptcena.) Hemispherical ; sides, with prominent, rugose ears ; with obtuse, 
radiating striae and a few lines of growth. 
2, 3. L. Scabricula. {Rough Leptcena.) V. Plate LHI Fig. 14. 
4. L. Concinna. {Neat Leptcena.) Semi-cylindrical; smaller valve concave, deeply inserted; larger valve 
convex; neatly striated and spined longitudinally; smooth, polished. 
5. L. Lirata. {Ridged Leptcena.) Sub-orbicular; umbo large, produced ; larger valve, with longitudinal 
sulci and blunt ridges. 
6. L. Spinosa. {Spinous Leptcena.) V. Plate LHI.*, Fig. 11. 
7. L. Quincuncialis. {Squarish Leptcena.) Sub-orbicular ; cardinal area flat ; beak large, prominent ; sides 
rounded ; with longitudinal ribs, intersected by remote lines of growth. 
8. L. Pustulosa. {Pustulous Leptcena.) Orbicular, inflated, with transverse sulci ; beak prominent, acute ; 
with some pustule-like tubercles ; ears angular, sulcated, without spines. 
9. 19. L. Martini. {Martin’s Leptcena.) Semi-cylindrical; hinge-line produced; umbo inflated; with 
flattened base and many, filiform, longitudinal striae ; lesser valve fiattish, deeply inserted; auricles distinct, 
with two rows of spines. 
11. L. Antiquata. {Antiquated Leptcena.) Semi-cylindrical; hinge-line ending in auriform processes; sides 
parallel ; umbo large, produced ; larger valve inflated ; smaller valve flattish ; mesial sulcus wide ; with radiating 
ribs, reticulated at umbo by concentric undulations. 
12. L. Gigantea. {Gigantic Leptcena.) Transversely elongated, inflated; hinge-line parallel, ending in 
auriform processes; with radiating, obtuse ribs and waved striae. 
13. 14. L. Calva. {Smooth Leptcena.) Sub-quadrangular ; hinge-line parallel, with a row of spines on each 
side ; beak large, incurved; larger valve inflated, with deep mesial sulcus; smooth, with equidistant lines of 
growth ; lesser valve smooth, with transverse lines of growth. 
15. L. Mesoloba. {Middle-lobed Leptcena.) Sub-ovate; auricles obtusely angled ; with mesial ridge on 
convex valve and corresponding sulcus on other ; smooth, wrinkled. 
16. L. Laxispina. ( Wide-spined Leptcena.) Hemispherical; margin regular; lower valve convex, without 
mesial sulcus ; with slender spines, incurved outward on hinge-line. 
17. L. Muricata. {Muricated Leptcena.) , Orbicular; umbo large, produced; back flattened; with broad, 
strong, continuous ridges, and regular, blunt murications. 
18. L. Setosa. {Bristled Leptcena.) Semi-circular; hinge-line parallel, with auriform processes ; with strong, 
longitudinal striae, and needle-shaped spines. 
20, 21, 22, 24. L. Punctata. {Punctured Leptcena.) Obovate; larger valve gibbose, with deep, mesial 
sulcus ; with concentric, laminar ridges and sulci; with many, minute spines ; smaller valve flat, with concentric 
sulci and flattened ridges. 
23. L. Ovalis. {Oval Leptcena.) Oblong ; hinge-line arcuated ; larger valve gibbose ; umbo large, produced ; 
mesial sulcus slight, with concentric sulci; with many, spinulose puncta; smaller valve flat, with a few, 
concentric sulci. 
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