EXPLANATION OF PLATE X. 



VOLUTODEKMA BIPLICATA Gabb (p. 90). 



Figs. 1-2. Opposite views of the type speoiinen from the Acad. Nat. Set., Phila. 



VOLUTODEKMA OVATA Whitf. (p. 91). 



3,4. Opposite views of the specimen showing the plications aud abrupt shoulder of the volu- 

 tions. Collection of the Am. Mus. Nat. Hist., New York City. 



VoLUTA ? Delawakensis Gabb (p. 84). 



5. Back virfw of the smaller cast used by Mr. Gabb. 

 6, 7. Two views of the larger cast, both types and from the Acad. Nat. Sci., Phila. 

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