PLATE 53. 



Fig. 1, 2. 437. 16. Lingula lamellata. ( Pag. 249.) 



1. A specimen preserving tlie shell, and having the beak acute. 



2. A specimen vvfliere the shell is removed, leaving the surface with faint concentric lines and a few longi- 



tudinal striiB. 



Fig. 3. 610. 8. Orbicula tenuilamellata. (Pag. 2-50.) 



Fig. 4. 611. 9. OllBICULA? SQUAMTFORBIIS. ( P^g 250.) 



4 a. An individual of the natural size. 



4 b. The same enlarged, to show more distinctly the characters of the surface. 



Fig. 5. 618. 24. Leptjena transversalis. (Pag. 256.) 



5 a, b, c. Dorsal and ventral views of two small individuals, where the hinge-line is much extended into acute 



poirits. 

 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 tlie 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 k. Tlie interior of the ventral valve, showing the strong parallel laminae, and prominent points on either 



side for the muscular attachment. 



5 /. A profile or cardinal view of the preceding specimen, showing the strong elevated lamina; for muscular 



attachment. 



Fig. 6. 448. 23. Lept^na depressa. (Pag. 257.) 



6 a, b, c. Dorsal and ventral views of young specimens, where ouly 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 k. The interior of the shell, showing the punctate surface. 

 6 I. The exterior striated surface, with fine concentric striae crossing them. 



Fig. 7. 619. 25. Lept^na striata. (Pag. 259.) 



Fig. 8, 9, 10. 620. 26. I.EPTiENA subplana. (Pag. 259.) 



8 a. The interior of the convex valve of a young individual, where the width is greater than the length. 



8 6. A specimen from which the shell is partially removed. 8 c. The strias enlarged. 



9 a. Cast of the ventral valve, apparently identical with the preceding, showing the muscular impression and 



the remains of the dental lamina? . 



9 b. The interior of the valve of another specimen, showing the dental laminje of the same form as in the 



preceding figure. 



10 a. A large individual having sharp prominent striie which are dichotomous, and crossed by finer strife, 



which remain in the depressions only. 

 10 c. Several of the strias enlarged, showing the concentric strife. 

 10 6. Cardinal view of another similar specimen, showing the narrow extended area and foramen. 



