PLATE 26. 



P»ge 



Figs. 1-8. Pboductella iiystricila 17H 



I, 2. InipressioDg of dorsal valves, one of them sliuwing the truncate apex, and both of them 



sliowing tlie marks of the narrow linear area. 



8, 4, 5. Casts of ventral valves, the curvetl lines showing the relative convexity of the speci- 

 mens. 



C. A restored specimen, showing the spines am preserved in impressions in the sandstone. 



V. The interior of a dorsal valve enlarged to two diameters, showing the form of the cardinal 

 process and the small dental sockets. 



8. A cardinal view of a cast of a ventral valve, showing the narrow area and bilobed apexj en- 

 larged to two diameters. 



Figs. 9 - 15. Prodcctella costatula 180 



9. The interior of a dorsal valve, with an enlarged cardinal process from another individual. 

 10. A front view of the ventral valve of a narrow individual, showing elongate pustules at the 

 bases of the spines, but with no continuous costa). 



II, 12. The front view, and profile of an older individual, showing continuous costse. 



13 - 15. Front view, profile, and cardinal view of another individual, showing continuous eostsv. 



Figs. \(i - 23. Productella arctirostrata 18*2 



10, 17. .^n impression of the exterior of a dorsal valve, with piv^fllc of the same. 



18. The impression of a dorsal valve, showing strong concentric wrinkles, with an impression of 



the cardinal process; having fewer pustules on the surface than fig. 16. 

 19-21. Front, profile and cardinal views of a ventral valve, of the same variety of form and 



surface marking, as fig. l(i. 

 22, 23. Two views of the typical specimen of this species; the ventral valve is distorted 



to some extent, but the mesial depression is apparently a natural feature. 



Figs. 24 - 28. Productella ^ialveata 18ii 



24. A small specimen of a ventral valve, showing numerous concentric wrinkles, with a greater 



number of spines towards the front than usual in specimens of this species. 



25. A young individual, with incon.«i)icuous wrinkles, and a well defined mesial sinus. 

 2t). A larger individual, which is nearly destitute of a sinus. 



27. A larger individual, with distinct wrinkles and spiue-Uuses on the cardinal margin, with a few 



siniilur mstrks on one side, in front; llie mesial sinus is but faintly developed. 



28. An imperfect specimen, with faint concentric wrinkles and numerous spiniferous tubercles 



near the front; the sinus is strongly developed. 



Fig». 29 - 42. Productella onusta 184 



29. The interior of the dorsal valve of a young individual, showing the cardinal process and 



socket ridges. 

 80. The interior of a large dorsal valve, showing concentric wrinkles, the cardinal process and 

 median septum, with the muscular and vascular impressions. 



31. The interior of a dorsal valve from whicli the shell is partially e.xfoliated; the cardinal pro- 



cess is much stronger than in fig. 30. 



32. A cardinal view of the specimen fig. 31, siiowing the convexity of the inner surface. 



83. A fragment of a large dorsil valve, showing the termination of tlie renil'orm vascular irapres- 



siiin on one side, with an oblique vascular impression diverging on each side from the 

 termination of the mesial septum. The outline is restored to sliow the relation of the 

 parts prest'rved. 



84. A dorsal valve which has been doubtftilly referred to this species; it is nearly flat, with a 



few obscure wrinkles, and a cardinal process similar to others of this species. 

 35. The ventral valve of a young individual. 



8ti, 87, 88. Ventral and cardinal views, and profile of a large ventral valve of this species. 

 89. 40. Cardinal views of casts of two ventral valves, sliowing the muscular markings, and in 



39, the deep pits on the sides of the beak left by the removal of the dental lamellas. 



41. An enlargement of the surface of the shell, showing round spine-bases, and irregular lines of 



growth. 



42. An enlargi-ment of the surface of the cast of a ventral valve, showing the irregular striatioa 



aiul distant pimcta. 



