EXPLANATION OF PLATE X. 
VOLUTODERMA BIPLICATA Gabb (p. 90). 
Figs. 1-2. Opposite views of the type specimen from the Acad. Nat. Sci., Phila. 
VOLUTODERMA OVATA Whitf. (p. 91). 
3,4. Opposite views of the specimen showing the plications and abrupt shoulder of the volu- 
tions. Collection of the Am. Mus. Nat. Hist., New York City. 
VoLuTa ? DELAWARENSIS Gabb (p. 84). 
5. Back view 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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