PLATE LXXXYI. 
1. Cyrena Obovata. (Egg-ovate Gyrena) Obovate, gibbose; anterior side obtuse; beaks large; surface, with strongish lines 
of growth. 
2. C. Deperdita. (Lost Gyrena.) Transversely oval, gibbose, umbonate; anterior side angulated; surface, with elevated lines 
of gi’owth ; hinge, with three, bifid, cardinal and two lateral teeth. 
3. C. Cuneiformis. (Wedge-shaped Cyrena.) Transversely cuneiform; anterior side angulated; surface, with many, fine lines 
of growth. 
4. Cytherea Nitidula. (Shining Gytherea.) Ovately rounded, tumid, smooth, shining; surface, with faint, transverse stria3; 
lnnule cor diform; hinge, with three teeth. 
5. C. Trigonula. (Trigonal Cyrena.) Ovately trigonal, sub-equilateral, thick; with sub-imbricated, transverse lines of growth; 
with three, cardinal teeth in each valve; lateral teeth serrated; umbones obtuse; margin plain. 
6. Cyelas Angulata. (Angular Gyclas.) Sub-triangular, beaks prominent; anterior side rounded; posterior side truncated; 
surface smooth, with shallow lines of growth. 
7. C. Major. ( Greater • Gyclas.) Sub-rotund, convex; beaks central, produced; basal line undulous ; surface smooth. 
8,9. C. Gibbosa. (Gibbous Gyclas.) Transversely ovate; beaks central, large, produced; anterior side rounded; posterior side 
truncated, acute below; surface smooth. 
10. Piseidium Amnicum. (Favourite Piscidium.) Obliquely oval; beaks tumid, produced; surface, with many, concentric, 
striated sulci. 
11. P. Pusillum. (Weak Piscidium.) Ovate, orbicular, sub-compressed; beaks prominent, obtuse; sides flattened; surface, 
with fine, concentric stria). 
12. C. Elongata. (Elongated Gyclas) Transversely elongated; beaks central; posterior side obliquely truncated; dorsal aud 
basal lines straight, parallel; surface smooth, with three or four lines of growth. 
13. C. Subquadrata. (Half-square Gyclas.) Transverselyeiongated; an oblong square; sides straight; beaks central, small ; 
back and base straight, parallel; surface, with concentric sulci. 
14. C. Media. (Middle Gyclas.) Depressed, thick, transversely obovate; anterior side small; surface smooth; both valves 
with one tooth under beaks. 
15. Cytherea Tellinaria. (Tellina-like Cytherea.) Transversely ovate, trigonal, smooth, sub-striated, sinuatod; lunule large, 
ovately oblong; bingo, with three cardinal teeth. 
16. C. Parva. (Small Gyclas.) Sub-orbicular, oblique; posterior side narrowed below; surface smooth. 
17. Cyprina Morrisii. (Morris's Gyprina) Sub-orbicular, gibbose; beaks obtuse, incurved; surface, with shallow, concentric 
lines of growth; back straight; base arcuated. 
18. C. Rostrata. (Beaked Cyprina.) Obliquely triangular; beaks large, produced, incurved; side beneath beaks concave, 
hollow; dorsal line nearly straight; posterior side lengthened, with a ridge from beaks to margin; basal line arcuated; surface 
smooth. 
19. C. Pusilla. (Slender Cytherea) Small, orbicular, sub-transverse; with many, transverse stria) ; umbones small, recurved; 
without lunule; hinge, with two teeth in one valve and three in the other. 
20. C. Cornea. (Horny Cyelas) Sub-globose, vcntricoso; beaks obtuse, with very fine, concentric stria). 
21. C. Suleataria. (Furrowed Cytherea) Ovate, tumid, inequilateral; with transverse sulci; umbones small; lunule large, 
ovate; hinge, with three teeth ; posterior one of left valve bifid; that of right valve lamellose. 
22. C. Transversa. (Transverse Gy thei'ea.) Transverselyeiongated, oblong-ovate, gibbose; surface smooth, with concentric 
lines of growth ; beaks incurved; lunette elongated, narrow. 
23. C. Trigonula. (Trigonal Cytherea.) Trigonal, sub-equilateral, smooth, transversely sub-striated; umbones small, acumi¬ 
nated; lunule cordiform, deep ; hinge, with three teeth. 
24. C. Obliqua. (Oblique Gytherea.) Ovate, oblique, tumid, sub-quadrate, inequilateral; umbones recurved; lunule large, 
cordiform; with many, transverse stria); hinge, with three teeth, posterior one bifid. 
25. C. Eryeinoides. (Erycina-like Gytherea.) Transversely ovate, sub-depressed; with many, transverse sulci; lunule small, 
smooth; hinge, with three teeth, posterior one bifid. 
26. C. Rivieola. (River Cyelas) Transversely ovate, gibbose; beaks central; sides rounded ; surface, with strong, concent ric 
stria). 
27. P. Henslowiana. (Hensloiv's Piscidium.) Obliquely oval, inflated; beaks tumid, produced, tuberculated; surface, wit h 
well-defined, concentric grooves. 
28. C. Membranacea. (Membranaceous Gyclas.) Depressed, thin, transversely ovate; anterior side small; posterior side 
pointed. 
29. C. Vulgaris. (Common Gyprina) Sub-orbicular, gibbose; beaks large; surface, with many, concentric striae; dorsal and 
basal lines arcuated. 
30. C. Pulchra. (Beautiful Gyrena) Sub-orbicular, convex; posterior side truncated; surface smooth; hinge, with one, sharp- 
edged and two, bifid teeth; shell thin, slender. 
31. C. Rustica. (Rude Gyprina) Sub-orbicular, transverse, gibbose; beaks obtuse; anterior side narrowed; dorsal liue 
straight; base arcuated; surface smooth, with strongly marked lines of growth. 
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