PLATE 20. 



* 



Ficr, 1. 434. 13. LlNGULA 08L0NGA. { Pag. 54.) 



1 a. .V youug individual of this species. 1 b. A specimen of the ordinary size of tliis sliell. 



1 c. Specimen longer tlian the usual form. 



1 d. A portion of tlie surl^ce enlarged, showing the longitudinal striie and concentric lines of growth. 



Fig. 2. 435. 14. LiNGULA oblata. ( Pag. 54.) 



2 a. A figure cU' an individual of the ordinary size of thi.s species. 

 2 b. A portion of tlie .surface enlarged. 



2 c. Tlie inner surface of a specimen, showing the longitudinal depressed line. 



Fig. 3. 436. 15. Li.ngula perovata. (Pag. 55.) 



3 a. Specimen natural size. 3 b. The specimen enlarged. 



Fig. 4. 437. 16. LiNGULA lamell.ita. (Pag. 55.) 



4 o. A single valve, preserving the form and character of the shell very perfectly. 

 4 4. A portion of the surface enlarged. 



Fig. 5. 43S. 17. Lingula acutirostra. ( Pag. 56.) 



Fig. 6. 439. 21. Okthis ciKcuLus. ( Pag. £6.) 



6 a. A view of the ventral valve, showing the beak of the dorsal valve. 



6 b. View of the dor.sal valve. 6 c. Profile view of the shell. 6 d. Front view of the same. 



6 e. Cardinal view of the same. 6 /. Cast of the dorsal valve of this species. 



6 g. The striaj enlarged, showing their mode of bifurcation and increase. 



Fig. 7. 440. 22. Orthis elegantulaV Var. (Pag. 57.) 



7 a. Dorsal valve of a specimen of medium size, somewhat distorted by pressure. 



7 b. Uinge-line and beak of dorsal valve. 7 c. Dorsal valve of a large individual. 



7 e. The east of a dorsal valve of a small individual. 



7 /. Cast of the dorsal valve somewhat compressed. 



7 g. Dorsal valve with the shell partially removed. 7 h. Dorsal area of 7 g. 



7 i. Showing the flattened stria:. 7 k. Several of the stria- enlarged. 



Fig. 8. 441. 23. Orthis trinttcleus. (Pag. 58.) 



8 a. Interior of ventral v.alve. 8 6. Cast of ventral valve. 



Fig. 9. 442. 24. Orthis tenuidens. ( Pag. 58.) 



9 a. Ventral valve with the shell partially removed. 



9 6. A more perfect cast, showing the form of the muscular impression. 



9 c. The last enlarged. 9 <f . The impression of a dorsal valve. 9 c. The last enlarged. 



Fig. 10. 469. 40. Atrypa gibbosa. ( Pag. 79.) 



V) a I; c. Casts of the dorsal valve. 10 b. Cast of the ventral valve. 



10 d. Cast of the dorsal valve, differing slightly from the preceding. 

 10 c. Profile view of the dorsal valve. 



