PLATE 55. 



Page 

 Fig8.1-8. RlIYNCHONELLA (StENOCISMA) EXIMIA 348 



1. Dorsal view of a small individual of the siK'cies, showing no mesial elevation. 



2, 8. Dorsal and ventral views of a larger s|>ecimeu. 



4-8. Dorsal, ventral, profile, cardinal and fVont views of a cast. 



Figs. 9-16. Rhynchonella (Stknocisma) STEPHANi 349 



9. Ventral valve of a young individual. 



10. Ventral view of a cast of a larger sj>ecinicn. 



11, 12. Profile and front views of the cast of a dorsal valve, having narrow angular i>lication9. 

 18-15. Dorsal, cardinal, and profile views of a cast, showing the characters of the dorsal 



portion of the hinge. 

 16. Ventral view of a cast, showing the muscular impressions. 



Figs. 17-25. Rhynchonella (Stenocisma) duplicata 350 



17-20. Dorsal, ventral, profile and front views of a characteristic specimen of ordinary size. 

 21, 22 Casts of dorsal valves, showing muscular impressions, etc. 

 28. Cast of a ventral valve, showing muscular impressions. 



24. An enlarged figure of a gutta-i>erclia impression taken from specimen, fig. 22, showing the 



mediaa septum, hinge-plate and crura, and a thickening of the cardinal portion oi the 

 interior. 



25. An enlarged figure of a gutta-percha impression of specimen, fig. 23, showing muscular 



impression, teeth, etc. 



Figs. 26-39. Rhynchonella (Stenocisma) conteacta 351 



26. Ventral valve of a small specimen with fine plications. 



27. Dorsal valve of a specimen having stronger plications. 



28. Ventral valve of a specimen, showing only two plications in the mesial sinns. 



29-83. Dorsal, ventral, profile, front and cardinal views of a characteristic specimen of the 



prevailing size. 

 84, 35. Dorsal and cardinal views of a cast, showing the cavities left by the removal of the 



hinge-plate, teeth, septum, etc. 



36. Ventral valve, showing four plications in the sinus. 



37. Cast of a ventral valve of unusually large size. 



38. Enlarged view of the cast of a ventral valve, showing muscular impression and filling of the 



rostral cavity. From the Hamilton group, four miles south of Cardifl', Onondaga Co., 

 N. Y. 



39. Ventral valve of a specimen of this species, from the Waverly sandstones of Ohio. 



Figs. 40-46. Rhynchonella (Stenocis.ma) okbic Claris 353 



40. Cast of a dorsal valve, showing the triangular filling of the fissure in the hinge-plate. 



41. Cast of a dorsal valve of a broader form, which approaches very closaly to R. contracta. 



42. Cardinal view of the cast of a dorsal valve. 



43. Cardinal view of a cast, showing the cavities left by the removal of the hinge-plate, teeth, etc. 



44. Ventral view of a cast, showing muscular impressions. 



45. Dorsal view of the cast of a large siK;cimen from Cliautauque Co., N. Y. The otherfigures 



of the 8i>ecie8 are all from bi)ecimens collected near Meadville, Pa. 



46. Enlargement from the cast of a ventral valve, showing muscular impressions ami dental 



cavities. 



Fig». 47 - 52, RHrNCHONELLA (Stenocisma) sappho var 354 



47. 48. Views of dorsal valves, showing some variation in form and number of plications. 

 49-61. Ventral valves of this species. 



62. Front view of a crushed specimen. 



