PLATE 53. 
Fig. 1, 2. 437. 16. Lingula lamellata. (Pag. 249.) 
1. A specimen preserving the shell, and having the beak acute. 
2. A specimen where the shell is removed, leaving the surface with faint concentric lines and a few longi¬ 
tudinal striae. 
Fig. 3. 610. 8. Orbicula tengilamellata. 
Fig. 4. 611. 9. Orbiuuua-?- squamiformis. 
4 a. An individual of the natural size. 
4 b. The same enlarged, to show more distinctly the characters of the surface. 
(Pag. 250.) 
(Pag. 250.) 
Fig. 5. 618. 24. Lept;ena transversalts. (Pag. 256.) 
5 a, b, c. Dorsal and ventral views of two small individuals, where the hinge-line is much extended into acute 
points. 
5 d. A larger specimen, where the hinge-line is slightly extended on one side, while the other is less extended. 
5 e, f. Dorsal and ventral views of a large individual, having the hinge-line slightly extended. 
5 g. Cardinal view, showing the extreme convexity of the dorsal valve, and the inflection of the cardinal 
margin. 
5 h. An enlargement of the surface, showing the coarser striae with intermediate finer ones. 
5 i. The interior, showing a striato-punctate character, with reticulations like the lines of bloodvessels. 
5 fc. The interior of the ventral valve, showing the strong parallel laminae, and prominent points on either 
side for the muscular attachment. 
5 Z. A profile or cardinal view of the preceding specimen, showing the strong elevated laminae for muscular 
attachment. 
Fig. 
6. 448. 23. Leptjena depressa. (Pag. 257.) 
6 a, b, c. Dorsal and ventral views of young specimens, where only a narrow portion of the margin is de¬ 
flected. 
6 d. A larger individual. 
6 e. An individual of the ordinary full grown size, regarded as a mature form. 
6 /. A very large individual, having the undulations more numerous, but less conpicuous than in fig. 6 e. 
6 g, h. Dorsal view of two small individuals, showing a slight difference in the character of the foramen, etc. 
6 i. The interior of a ventral valve, showing the muscular impression and dental laminae. 
6 Zc. The interior of the shell, showing the punctate surface. 
6 Z. The exterior striated_surface, with fine concentric striae crossing them. 
Fig. 7. 619. 25. Lepta:na striata. (Pag. 259.) 
Fig. 8, 9, 10. 620. 26. Leptjena subplana. (Pag. 259.) 
8 a. The interior of the convex valve of a young individual, where the width is greater than the length. 
8 b. A specimen from which the shell is partially removed. 8 c. The striae enlarged. 
9 a. Cast of the ventral valve, apparently identical with the preceding, showing the muscular impression and 
the remains of the dental laminae. 
9 b. The interior of the valve of another specimen, showing the dental laminae of the same form as in the 
preceding figure. 
10 a. A large individual having sharp prominent striae which are dichotomous, and crossed by finer striae, 
which remain in the depressions only. 
10 c. Several of the striae enlarged, showing the concentric striae. 
10 b. Cardinal view of another similar specimen, showing the narrow extended area and foramen. 
