PKODUCTUS AND A SMALL SPIRLFERLNA. 465 



Fig. 15. A more transversely elongated ventral valve, with spines, exterior 



view. 

 16, 17. Portions of the exterior of two ventral valves, showing the 



hinge-spines, b. 

 18, 19. Exterior of two dorsal valves, showing the cardinal process and 



concentric wrinkles. 



20. Hinge-line, and portions of both dorsal and ventral valves united, 



with one of the large hinge-spines in position. 



21. Interior of the dorsal valve : aa, ridges from the cardinal process to 

 the cardinal angles ; b, b, divisions of the mesial ridge ; c, enclosed 

 space. 



22. Exterior of the dorsal valve, with the cardinal process, concentric 



wrinkles, and traces of the reticulate character assumed by the 

 latter. 



23. Interior of a portion of the dorsal valve : a & c similar to fig. 21 ; 



d, d, adductor impressions. 



24. Similar to fig. 22. 



Spirifekina, 



sp. 



Fig. 25. Dorsal valve, showing the mesial fold. 



26. Ventral valve, showing the sinus. 



27. Hinge and fissure &c. 



Stropiialosia (Orthotrix) Goldfussi, Minister. 



Fig. 28. After Geinitz, showing the form clinging by its umbonal spines to 

 one of the large spines of a Productus horridus. ( Die Verstein. d. 

 deuts. Zechst. pi. 2. f. 27.) 

 28 a. The same, enlarged. 



(N.B. Tne natural size of the fossils is shown, as nearly as possible, by the in - 

 dicators placed near the figures.) 



£ 2 



