PLATE 53. 



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



1. A specimen preserving the shell, ami having the boak acute. 



2. A spcciinrn where the shell is removed, leaving tlie surface with faint concentric liTies and a few longi- 



tudinal stria;. 



Fig. 3. 610. 8. Orbicula tenlmlamellata. ( Pag. 250.) 



Fig. 4. 611. 9. Obbichla? squamiformis. (Pag. 250.) 



4 a. An individiial of the natural size. 



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



Fig. 5. G18. 24. Lept^ena transversalis. (Pag. 256.) 



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

 points. 



5 (2. 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 sliglitly extended. 



5 g. Cardinal view, showing the extreme convexity of the dorsal valve, and the intleclion of the cardinal 



margin. 

 5 h. An enlargement of the surface, showing the coarser stria; with intermediate finer ones. 



5 I. The interior, showing a striate. punctate character, with reticulations like the lines of bloodvessels. 



6 k. Tlie interior of the ventral valve, showing the strong parallel lamina;, and prominent points on either 



side for the muscular attachment. 

 6 /. A profile or cardinal view of the preceding speeimeuj showing the strong elevated laminae for mu.scular 

 attachment. 



Fig. 6. 448. 23. Leptjena depressa. (Pag. 257.) 



6 a, b, c. Dors,al 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. 



G /. A very large individual, having the undulations more numerous, but less conpicuous than in fig. c. 

 6 g, A. Dorsal view of two small individuals, showing a slight difTcrence in the character of the foramen, etc. 

 6 t. The interior of a ventral valve, showing the muscular impression and dental laminae. 

 6 fc. The interior of the .shell, showing the punctate surface. 

 6 /. The exterior striated surface, with fine concentric stria; crossing them. 



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



Fig. 8, 9, 10. 620. 26. Lept^na subplana. ( Pag. 259.) 



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



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



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



the remains of the dental lamina;. 



9 6. The interior of the valve of another specimen, showing the dental lamina; of the same form as in the 



preceding figure. 



10 a. A large individual having sharp prominent strise which .ire dichotomous, and crossed by finer stria;, 



which remain in the depressions only. 

 10 c. Several of the stria; enlarged, showing the concentric stria;. 

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



