PLATE LVII 



PAGE 



Fig. 1. SPIKIFEB DISJUNCTUS Sowerby 593 



Internal cast of conjoined valves with extremely extended cardinal 

 angles. Jennings formation, Chemung member, near Deer Park. 



Figs. 2-5. SPIRIFEB MESASTEIALIS Hall 596 



2. Cast of interior of ventral valve. Near Pawpaw, W. Va. 



3. Cast of interior of dorsal valve. National Road, east of Millstone, 



2444. 



4. Enlargement of portion of surface of dorsal valve. Wills Creek 



Station, Penna. 



5. Dorsal valve. National Road, east of Millstone. 



Jennings formation, Chemung member. 



Figs. 6-10. SPIKIFEB MARCYI VAR. SUPERSTES n. var 597 



6. Portion of cast of interior of dorsal valve, enlarged X 2, showing 



muscular scars and hinge. B. & O. Railroad cut, Rocky Run, 7 

 miles southeast of Cumberland. 



7. Enlargement of a portion of surface showing granulose plications. 



X 5. National Road, Polish Mountain. 



8. Cast of interior of dorsal valve. National Road, Polish Mountain, 



above sixth turn. 



9. Cast of interior of dorsal valve with shorter wings. National Road 



on Green Ridge, 2690. 



10. Posterior view showing cardinal area of ventral valve with partially 



filled delthyrium. Associated with fig. 9. 



11. Posterior view of cast of interior of ventral valve showing strength 



of dental plates. Associated with fig. 9. 



Jennings formation, Figs. 6, 7 from near base of Parkhead 

 member, Figs. 8-11 from Chemung member. 



140 



