PLATE LII. 
1. Spirifer Squamosa. ( Scaly Spirifer.) Depressed, oblong-ovate; mesial fold small; smooth, with transverse 
imbrications; umbones approximate. 
2. Orthis Filaria. (Thready Or this.) Elongated, pocket-shaped; hinge-line short; cardinal area narrow ; umbones 
blunted; with wide-set, filamentary processes. 
3. S. Elongata. (Elongated Spirifer.) Elongated, pentahedral; sides flat, smooth; with many, longitudinal radia¬ 
tions ; mesial sulcus shallow; base flat, straight. 
4. S. Planosulcata. (Flat-furro'ived Spirifer.) Pentahedral, depressed ; central sulci of each valve flattened; umbones 
approximate. 
5. S. Expansa. (Expanded Spirifer.) Transversely sub-ovate, compressed; without mesial fold; with fine, longi¬ 
tudinal i*adiations, crossed by concentric striae. 
6. S. Resupinata. (Resupient Spirifer.) Transversely elliptical; umbones small, approximate; upper valve depressed 
in middle ; lower valve concave ; with many, longitudinal striae. 
7. S. Glabistria. (Smooth-striated Spirifer.) Transversely oblong ; umbones obtuse, approximate; with longitudinal 
radiating striae; mesial fold produced. 
8. S. Radialis. (Radiating Spirifer.) Semi-elliptical, transversely elongated; hinge-line parallel; base semi-circular* 
with strong, divergent ribs, crossed by imbricated lamellae; umbones obtuse. 
9. 10. Terebratula Hastata. (Spear-shaped Terebratula.) Elongated, elliptical, semi-compressed; valves equal- 
base truncated, indented ; edges sharp. 
11.20. T. Indentata. (Indented Terebratula.) Elliptical, smooth, inflated; valves convex; beak small, incurved- 
base, with deep notch ; valves, with broad sulci. 
12. S. Globularis. (Globular Spirifer.) Sub-globose, smooth; umbones obtuse, approximate; mesial fold broad. 
13. Orthis Connivens. (Con7iivant Orthis.) Sub-globose; with undulated margin; with coarse, divergent, longi- 
tudinal striae. 
14, 21. T. Triquetra. (Triangular Terebratula.) Sub-orbicular: valves convex; beak produced, incurved, keel¬ 
shaped ; perforation triangular; base indented ; edge of upper valve level, sharp ; surface smooth. 
15, 16. T. Perovalis. (Somewhat Oval Terebratula.) Sub-ovate; valves convex; smooth; beak incurved, acute- 
margin obtuse; base, with two sinuses. 
17, 18. T. Globata. (Globular Terebratula.) 
19. Orthis Arachnoidea. (Spider's-web Orthis.) Scutiform, compressed; hinge-lino parallel; umbones minute 
blunt; upper valve convex; with fine, sharp, divergent striae, crossed by remote lines of growth. 
22, 23. T. Emarginata. (Emarginate Terebratula.) Sub-rhomboidal; larger valve convex ; smaller one flat; base 
emarginate or with two angles. 
24. Leptsena Papilionacea. (Butterfly-like Leptama.) Wide, semi-elliptical; hinge-line parallel; umbones minute • 
with fine, longitudinal striro; crenulated in young state. 
25.20. T. Bullata. (Swelled Terebratula.) Orbicular, ventricose ; beak produced, incurved; base indented; edges 
level. 
27, 28. T. Obtusa. (Obtuse Terebratula.) Sub-orbicular, depressed; valves regularly convex, abruptly bent near 
edges; margin obtuse, square ; base broad, elevated. 
29, 30. T. Maxidata. (Combe Terebratula.) Sub-quadrangular, convex; umbo large, incurved; base, with two acute 
sinuses, and one obtuse one on each side; upper valve, with three sulci; lower valve, with two sulci; base rounded. 
31, 32. T. Sella. (Saddle-formed Terebratula.) Sub-quadrangular, or trigonal, convex ; beak obtuse, curved; sides 
compressed ; base elevated, narrow. 
33, 34. T. Elongata. (Elongated Terebratula.) Oval; valves equally convex ; beak small, acute, incurved : smooth. 
35, 36. T. Biplicata. (Two-plaited Terebratula.) Oblong, gibbose; beak large, incurved; sides rounded; base 
parallel, with two, distant plaits or obtuse ribs. 
37, 38. T. Bucculenta. (Full-cheeked Terebratula.) Squarish; valves equal; convex; beak short, incurved; sides 
convex ; edges level; base produced, truncated. 
39,40. T. Sacculus. (Little Bag Terebratula.) Obovate, gibbose; with broad, central sulcus, dividing larger valve 
into two lobes; smaller valve, with minute sinus at edge; beak small, sharp. 
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