PLATE LXVI.** 
1. Avicula Humata. (Buried Avicula.) Sub-depressed; valves very oblique; hinge-line long, straight; surface, with many, 
elevated, longitudinal ribs; beaks slightly protruding; edge crenulated; crossed by many, fine lines of growth; auricles of medium 
size. Length and breadth, about \ in. 
2. A. Pectinata. ( Pectinated Avicula.) Obliquely elongated, somewhat convex ; hinge-line straight, horizontal; beaks obtuse • 
auricles large; posterior one concave; anterior one convex, rounded; surface, with long and short, linear ridges. 
3. A. Diseors. (Discordant Avicula.) Smooth, oblique; anterior side short, acute; posterior one broad; one auricle large, the 
other small, parallel to hinge-line; beaks small, prominent. Length, $ in.; breadth, f in. 
4. 7, 8. A. Inflata. (Inflated Avicula.) Oblique, inflated, transversely oblong-ovate; hinge-line much on one side; auricle 
small, acute. Length, in.; breadth, i in. 
5,6. A. Binneyi. (Binneys Avicula.) Smooth, oblique; beaks prominent, acute; larger auricle, parallel with undefined 
hinge-line; the other small; hinge-line straight; centre of valves ventricose. Length, -fa in.; breadth, £ in. 
9, 10,11. A. Echinata. (Spinous Avicula.) Obovate, gibbose; deeper valve, with many, muricated ribs and unequal auricles- 
anterior one rectangular; flatter valve, with anterior auricle acute. 
12. A. Novemcostse. (Nine-ribbed Avicula.) Obliquely oval; hinge-line oblique; one ear minute, the other large; surface 
smooth, with nine, longitudinal, rounded ribs. 
13. A. Expansa. (Expanded Avicula.) Oblong-ovate, oblique; posterior side produced; anterior side short, curved; auricles 
well-defined, unequal; hinge-line oblique ; surface smooth, with about sixteen, rounded, longitudinal ribs. 
14. A. Ovalis. (Oval Avicula.) Oblong-oval; ears unequal; hinge-line oblique, straight; beaks produced; sides unequal 
gently rounded ; surface, with many, shallow, longitudinal sulci, and a few concentric lines of growth. 
15,16. A. Longicostata. (Long-ribbed Avicula.) Ovate, inequivalve; ears unequal; surface of lower valve with six, elevated 
narrow, longitudinal ribs, central, second, and sixth ribs being more raised; rib next the larger ear tripartite; intercostal spaces 
with fine, irregular, longitudinal strife, crossed towards base with lines of growth; surface of fiat valve, with five or six, longitudinal 
sulci, opposite ribs in other valve; intermediate spaces, with many, fine, longitudinal strise; margins plain, circular. 
17. A. Cygnipes. (Stvan's-foot Avicula.) Sub-quadrate, oblique; lower valve convex, the other fiat; hinge-line straight, 
oblique; umbo of convex valve rounded, obtuse; auricles unequal; surface, with four to five, longitudinal, curved-ribs, endin''- in 
acute points; intercostal spaces with fine, longitudinal strife; flat valve, with sulci corresponding in number to ribs of other valve 
with coarser longitudinal strife and apex, concentric lines of growth. 
18. A. Ovata. ( Ovate Avicula.) Convex, transversely ovate; posterior side elongated, obtuse; liinge-line long, forming part 
of posterior wing. 
19,20. A. Graphoides. (Graphite Avicula.) Obliquely elongated; convex valve ovate; beak produced, incurved; with two 
small, equal auricles; upper valve flat, sub-orbicular, with a single auricle. 
21. A. Elegantissima. (Very Elegant Avicula.) Transversely elongated; twice as long as broad; beaks produced, large 
rounded; anterior side short, straight; surface smooth, with seven to nine, longitudinal, smooth ribs in centre of valves. 
22. Gryphsea Bulla. (Vesicular Gryphcea.) Oblong, convex; beaks short, curved laterally; surface nearly smooth; form 
variable. 
23. 24. Ostrea Distorta. (Distorted Oyster.) Elongated, narrowed towards hinge; one valve fiat; surface of both valves smooth 
25, 26. G. Virgula. (Fallen Gryphcea.) Elongated, arcuated; one valve convex, with elevated lines, the other fiat. 
27. 0. Falcata. (Rooked Oyster.) Elongated, curved towards posterior side; one valve flat, thick ; surface, with many foliations. 
28. 0. Retusa. (Blunt Oyster.) Form very variable, but chiefly orbicular and greatly curved; thickish, plain in middle, with 
angular plaits on margin. 
29. A. Samuelsii. (Samuels 1 Avicula.) Semi-cirular; hinge-line straight; auricles undefined; beaks small, pointed; surface 
with rounded, longitudinal ribs, crossed by many, distinct lines of growth. Length, i in.; breadth, £ in. 
30. A. Radiata. (Bayed Avicula .) Sub-orbicular; hinge-line straight; beaks central; auricles unequal, acute; surface, with 
many, broadish ribs and narrow, intervening sulci; base rounded. 
31. A. Tessellata. (Tessellated Avicula.) Sub-quadrangular; hinge-line curving downwards; auricles large, unequal, sub¬ 
acute; surface, with eight to fifteen, rounded ridges ; margin scalloped. 
32. A. Sublobata. (Ralf-lobed Avicula.) Oval, oblique; hinge-line short, straight; small auricle on one side; surface with 
many, flat, narrow ribs and intervening sulci with fine, concentric striae. 
33. A. Bamburiensis. (Bambury Avicula.) Ovate, oblique; hinge-line oblique; auricles unequal; surface, with many, 
longitudinal ribs, with many, imbricated scales; basal margin scalloped; beaks obtuse. 
34. A. Cyeloptera. (Cyclops Avicula.) Sub-quadrangular; sides conical; surface smooth, with four or five, radiating rid"es ; 
basal margin rounded, scalloped; lines of growth slightly imbricated oil disc of valves. 
( 83 ) 
