PLATE LV 



PAGE 



Figs. 1-8. RHIPIDOMELLA EMARGINATA (Hall) 302 



1-4. Illustrations of the form and character of this variety. 

 5, 6. Interior of ventral and dorsal valves. 

 7, 8. Cast of the ventral and dorsal valve. 



Helderberg formation, Keyser member, Cumberland. (After 

 Hall.) 



Figs. 9-16. RHIPIDOMELLA OBLATA (Hall) 303 



9, 10. Ventral and dorsal valves. 



11. Profile of same. 



12. A small dorsal valve. 



13, 14. Interior of ventral and dorsal valves. 



15. Internal cast of the ventral valve, showing the muscular and 



vascular impressions. 



16. Cast of the dorsal valve, with impressions of the cardinal and 



brachial processes. 



New Scotland formation, New York. 



Figs. 17-19. RHIPIDOMELLA ASSIMILIS (Hall) 304 



17. Ventral valve. 



18. Dorsal view of a large shell. 



19. Interior of ventral valve. 



Helderberg formation, Becraft member, North Mountain, W. 

 Va. 



Fig. 20. RHIPIDOMELLA MVSCULOSA (Hall) 305 



Cast of interior of dorsal valve. Oriskany formation, New York. 



Figs. 21, 22. RHIPIDOMELLA MUSCULOSA VAR. ARCTISIXUATA Schuchert n. 



var 306 



21. Dorsal view. 



22. Ventral view of same. 



Oriskany formation, Ridgely member, Cumberland. 



Fig. 23. RHIPIDOMELLA MARYLANDICA Schuchert n. sp 306 



Interior cast of ventral valve. Oriskany formation, Ridgely member, 

 Williams road, near Cumberland. 



46 



