PLATE 38. 



Page 



Figs. 1 - 25. Spirifeka medi.^hs 227 



1 . Dorsal view of a small and very symmetrical specimen. 



•i, 3. Dorsal and c.irdinal views of a lftrp;er sjiccimen. having tlie extremities of the hinge line 



extended; fig. 3, shows the cardinal area and foramen. 

 4-6. Dorsal, cardinal and profile views of a more ventricose specimen, with a narrow incurvod 



area and strong concentric lines of growth. 

 7, 8. Dorsal and cardinal views of a specimen of medium size, having a higher area, which is 



but slightly incurved. 

 9- 11. Dorsal, profile and ventral views of a specimen having a high area and a semicircular 



dorsal valve. 

 12, 13. Dorsal and cardinal vie»-s of a specimen of slightly unsymmetrical form and rather 



strong ribs. 

 14-16. Dorsal, front and ventral views of a large specimen, having a small area and 



slightly projecting ventral beak. 

 17-20. "Dorsal, ventral, front and profile views of another specimen corresponding in size with 



the last, hut having a higher area, more projecting ventral beak, and higher mesial fold, 



presenting a strong contrast between figs. 17 and 14. and between 19 and 15. 

 21, 22. Cardinal views of two individuals with high areas, showing considerable variatien 



in the proportions of the deltidiuni; contrasting strongly in these respects with fig. 13. 

 28, 24. Interiors of dorsal valves, showing the muscular impressions, socket plates, etc. 

 25. Interior of a ventral valve, showing the mH.scular impre.ssion, cardinal area, teeth, and the 



callosity filling the apical portion of the dcltidial opening. 



