PLATE LIII.* 
I. Orthis Pecten. ( Pecten-formed Orthis.) Transversely ovate ; depressed, with many, radiating sulci. Length, g in.; breadth, 1$ in. 
2,3,4. Leptsena DistOPta. ( Distorted Leptccna.) Orbicular, convex; hinge-line parallel, with triangular area; beaks prominent; concen¬ 
trically undulated, with strong, longitudinal stria?; margin flattened. 
o. L. Margaritaeea. ( Pearly Leptccna.) Sub-orbicular, inflated; hinge-line parallel; beaks large, prominent; ears rounded; with many, 
radiating stria?; with two or three Bpines on ears and sides. 
6 . L. Plicatilis. ( Plicated Leptccna.) Transversely elongated; hinge-line parallel; umbo produced; with transverse, flexuous ribs and 
longitudinal stria?. 
7. L. Caperata. (Wrinkled Leptana.) Semi-elliptical, convex; margin deflected; lower valve convex ; upper one concave ; with concentric 
wrinkles; with adpressed spines. 
8 . 9. L. Scotica. {Scottish Leptccna .) Semi-circular; hinge-line parallel; umbo of larger valve prominent; both valves gibbose; sides 
expanded ; convex valve, with divergent stria?, and remote, parallel lines of growth ; shallow valve, with divergent strife, but without spines. 
10. L. Analoga. {Analogous Leptccna.) Semi-circular, compressed; hinge-line straight; lower valve convex near umbo; surface corrugated, 
with flexuous wrinkles ; crossed by straight, radiating stria?. Length, 1 in. 
II. L. Spinosa. ( Spinous LepUena.) Sub-orbicular, gibbous ; hinge-line short; convex valve, with cylindrical spines ; concave valve without 
spines ; with many, longitudinal stria?. 
12 . L. Tenuistriata. (Thin-striated Leptccna.) Semi-cylindrical; with many, longitudinal strine, crossed by twelve to fourteen, concentric 
convex sulci; sides expanded. 
13. L. Pug'ilis. ( Fighting LepUena.) Semi-circular; hinge, ending in spinous, auricular processes; umbo large, produced; with many, 
radiating stria? and longitudinal spines; with strong, irregular ribs, and a few, blunted spines towards the sides; margin much indented. 
14. L. Scabricula. (Rough LepUena.) Orbicular; hinge-line parallel; sides straight; beak large, prominent; smaller valve flat, with 
radiating strife; larger valve, with longitudinal, tuberculated strife ; mesial sulcus broad. 
15. L. Costata. (Ribbed Leptccna.) Transversely elongated; convex valve, with deep, mesial sulcus and longitudinal ribs, decussated by 
concentric sulci; base deflected ; each side, with two or three spines and small lobe. 
16. L. Comoides. (More Handsome Leptccna.) Semi-circular; globose near beak; disc inflated; with undulating stria? and large, longitu¬ 
dinal sulci; hinge-area flat; thick, rough internally. 
17. L. Membranacea. (Membranous Leptccna.) Semi-circular, very flat, thin; hinge-line parallel, produced, with spines; concentrically 
striated ; with undulating lines, with small spines. 
18. 19. L. Sordida. (Dilapidated Leptccna.) Transversely elongated, convex ; hinge-line, with rounded angles ; with irregular strife. 
20 . L. Sulcata. (Furrowed Leptccna.) Semi-cylindrical, short, convex above, with mesial sulcus; with spinose, longitudinal ridges. 
21 . L. Nodulosa. (Nodulous Leptwna.) Semi-circular; lower valve concentrically angulated; near border rectangularly reflected; with 
irregular, concentric ridges and sulci; with many, flexuous, longitudinal strife. 
22 . L. Pectenoidea. (Pecten-shaped Leptccna.) Orbicular hinge-line, ending in auricular processes; umbo large, prominent; with many 
smooth, longitudinal ribs, furcated towards base. J * 
23, 24. L. Sericea. (Silky Leptccna.) Elongated semi-circle ; larger valve convex, smaller depressed; base deflected at margin ; with silky 
lustre, and many, radiating strife; with obscure lines of growth. Length, ^ in.; breadth, 1 in. 
25. L. Lepisma. (Silvery Leptccna.) Semi-circular, convex; with silvery lustre; with a few, forked radiations; base deflected. Lenefh 
J in.; breadth, £ in. ** » 
narrow ribs (deceptions Leptccna.) Sub-triangular; hinge-line parallel, with auriform’processes; base pointed; surface, with remote, 
27. L. Edelburgensis. (AddUburgh Leptccna.) Semi-circular; hinge-line parallel, wide; beak somewhat produced; deeper valve convex- 
sides compressed ; with coarse, longitudinal strife ; spines few, or none. 
28. L. Englypha. (Well-carved Leptana.) Sub-triangular ; base obtuse; flat above; hinge-area long, straight, narrow ; with many, radiating 
ndges, and fine, elevated strne. Length of flat space, 1 in.; width, 2J in. b 
29. 30, 31. L. Deppessa. (Depressed LepUena.) Semi-circular; depressed above ; with longitudinal strife, crossed by transverse, narrow sulci• 
ninge-area long, with auriform processes ; upper valve rounded, with produced umbo; concave near margin ; front curved, deflected ; lower valve* 
concave in centre. Length of flat space, } in.; width, 1 } in. 
32,33. L. Hardrensis. (Hardrcn's LepUena.) Semi-circular; hinge-line straight, spinous; smaller valve concave; with many, radiating 
strife, crossed by lines of growth ; internally minutely punctated. 8 
L. Interrupta. (Interrupted Stricc Leptccna.) Semi-circular, gibbose; umbo slightly produced; larger valve, with longitudinal strife 
interrupted by concentric nbs. ° J r ’ 
35. L. Lsevigata. (Smooth Leptccna.) Semi-circular, depressed; hinge-line parallel; with short, auriform processes; smooth, shining, with 
radiating strife ; baso depressed. Length, £ in.; width, J in. b ’ 
undulations ^*1 ^e^ndM^] leptccna.) Orbicular; concave valve smooth ; convex valve gibbose, with reflected spines, and a few, concentric 
- ^ Latissima. (Very Broad Leptccna.) Transversely elongated, fusiform or convoluted; hinge-lino partly concealed by beak; umbo 
incurved; with coarse, longitudinal stria? and many, bristle-like spines. ’ ° 
longUudina? (Convoluted Leptccna.) Semi-circular; hinge-line, with auriform processes ; middle of lower valve convex ; with many, 
12* V Sarcinulata. (Little Truss Leptccna.) Semi-circular; hinge-line parallel; with eight or ten, simple, tubular spines; upper valve 
convex; lower valve concave; with many, radiating ribs. 6 1 
many^ 1 <fngidint!?^j2nous^strifc L e P tcCna -) Oblong, gibbose ; beak incurved; larger valve, divided into two lobes by deep, mesial sulcus; with 
with\ongitiid (Shouldered Leptccna.) Oblong, squarish, compressed; larger valve, with two cavities near beak ; smaller valve flattish; 
dinaf strhe ^ ersona ^ a * (Masked Leptccna.) Hemispherical; hinge-line arcuated; larger valve, with three, deep cavities ; smooth, with longitu- 
breadth Didyma. (Spread Atrypa.) Globular; umbones small; base emarginate; each valve, with central sulcus. Length and 
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