PLATE XCVI. 
1. Pholadomya Acuticosta. {Acute-ribbed Pholadomya.) Transversely oblong-oval; beaks obtuse, incurved ; 
anteriorly short, with four or five, keel-shaped, longitudinal ribs ; posteriorly narrowed ; basal line straight. 
2. P. Fidicula. {Harp Pholadomya.) Transversely elongated, gibbose, recurved x surface, with many, 
longitudinal ridges; anteriorly smooth, compressed. 
8. P. Obliquata. {Oblique Pholadomya.) Transversely elongated; posteriorly short; beaks incurved; 
anteriorly large, dilated, compressed towards margin ; surface, with concentric grooves and flat ribs. 
4. P. Ovalis. {Oval Pholadomya.) Transversely elongated, elliptical, straight, convex; front and back 
equally curved; sides rounded, gaping; with one sulcus posteriorly; surface, with about nine, longitudinal 
ridges. 
5. P. Decussata. {Decussated Pholadomya.) Cordiform, with broad, centrally elevated area, bounded by 
an obtuse keel posteriorly; beaks incurved ; surface, with longitudinal ribs, decussated by transverse ones. 
6. P. Murchisoni. {Murchison's Pholadomya.) Oval; beaks large; posteriorly short, with six or seven, 
obtusely round, longitudinal ribs, crossed by strong, undulating sulci. 
7. P. AJqualis. {Equal Pholadomya.) Transversely oval; equally rounded at both ends, straight; beaks 
obtuse, incurved, approximate; with six to eight, equal, divergent ribs from beaks to margin; basal line curved. 
8. P. Angustata. {Narroio Pholadomya.) Transversely elongated, gibbose ; anteriorly compressed ; surface, 
with about twelve, acute ribs, decussated by many, transverse striae ; shell thin. 
9. 10, 11,12. Fistulana Ampullaria. {Ample Fistulana.) Sheath sandy, bottle-shaped, continuous ; aperture 
internally bicarinated ; shell ovate, gaping; hiatus oval, with sinuosities. 
13. Teredo Navalis. {Ship Teredo.) Valves triangular, auriform behind, hemispherical when closed, with 
curved tooth on margin of umbonal region; surface of valves striated ; each with triangular projection in front, 
with flat, curved tooth ; tube flexuous. 
14,15. Teredina Personata. {Masque Teredina .) Valves transversely striated posteriorly; anteriorly smooth, 
with a few lines of growth ; accessory plate pentangular, smooth. 
16, 17, 18. T. Amphisbaena. {Blind-worm Teredo.) Valves unknown; tube lengthened, tapering, tortuous, 
smooth, composed of short segments with sharp edges, and concave, imbricated surfaces. 
19. Amphisbaena Articulata. {Articulated Amphisbcena.) See No. 16. 
20, 21. Gastrochaena Pholadia. {Pholas-like Gastrochama.) Transversely sub-ovate, cuneiform; broadly 
gaping anteriorly ; beaks prominent, obtuse; hinge, with obscure, laminar, transverse tooth in both valves. 
22, 23,24. G. Contorta. {Contorted Gastrochama.) Sheath claviform, bent almost at a right angle; aperture 
divided by two, opposite ridges ; valves ovate, elongated ; surface, with fine striae. 
25, 26, 27, 28. T. Discrepans. {Discrepant Teredina.) See No. 14. 
29, 30. G. Tortuosa. {Tortuous Gastrochama.) Length four times depth of both valves; obliquely lanceo¬ 
late, twisted ; hinge-line straight; surface smooth. 
31, 32, 33, 34. Teredo Antenautae. Valves, with transverse striae, those on anterior side, many, zig-zag, 
dentated, smooth, with dorsal, posterior, accessory valves testaceous. 
35, 36, 37. Clavag-ella Coronata. {Crowned Clavagella.) Tube straight, elongated, claviform, crowned with 
about eight, antler-like tubes; included valves oblong, sulcated, with strong lines of growth, gaping; beaks 
acute, large; pearlaceous internally. 
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