PLATE IV. 



Fig. 

 1 — i. 



5. 



;— 10. 



11. 



12. 

 13—15. 



16. 



17. 

 18. 



19. 



20. 



21. 



22. 

 23—25. 



26. 



27—29. 



30—31. 



(Permian Species.) 



Productus latirostratus, Howse = umbonillatus, King. Testiferous examples at different ages, 



from Tunstall, in the collection of Mr. Kirkby. 



— — Internal cast of the dorsal valve, natural size, from Dalton. Formerly 



in the collection of Mr. Howse, now in the Museum of Practical 

 Geology. Fig. 5 a is a gutta-percha impression of the same, 

 enlarged to show how the interior of the valve would be in its 

 natural condition. 



— — Internal cast of the interior of the dorsal valve, a portion of the 



beak of the ventral one still adhering, in which a narrow open 

 fissure is visible. Collection of Mr. Kirkby. 



— — Interior of the dorsal valve. Tunstall hill. Collection of Mr. Kirkby. 



— Different views of the cardinal process (enlarged), from Tunstall 

 hill. Collection of Mr. Kirkby. 



— Internal cast of the interior of the dorsal valve (fig. 11), and of the 

 ventral one (fig. 12), showing the position of the adductor (a), and 

 cardinal muscular impressions (r) ; from Dalton. Collection of 

 Mr. Howse. 



— Interior of the ventral valve, from a gutta-percha impression. 

 horridus, J. de C. Sowerby. Different ages, from Tunstall and Humbleton hills. 



Collection of Mr. Kirkby. 



— A very perfect example, from Tunstall hill, in the collection of Mr. 

 Howse. 



— A portion of one of the tubular spines, enlarged. 



— Young shell, from Humbleton hill, collection of Mr. Kirkby, showing 

 the great length of the cardinal spines. 



— Internal cast of the dorsal valve, with beak of the ventral one, from 

 Humbleton. Collection of Mr. Howse. 



— Internal cast of the dorsal valve, showing the muscular impressions. 

 This specimen is in an admirable state of preservation. 



— Interior of the dorsal valve, slightly enlarged, to better display all its 

 characters. 



— Interior of the ventral valve ; cardinal process considerably enlarged. 



— Figs. 23 and 24 are seen from the exterior of the ventral valve ; 

 fig. 25 from the inside. Collection of Mr. Kirkby. 



— Interior of the dorsal valve, from Tunstall hill. Collection of Mr- 

 Kirkby. 



Upper valve. From the collection of Mr. Howse and that of the 

 Museum of Practical Geology. Humbleton hill. 



Collection of Mr. Howse. 



Discina Koninckii, Geinitz 



Lingdla Credneri, Geinits. Natural size. From Ferry hill 



