EXPLANATION OF PLATE XXI. 
PERISSOLAX TRIVOLVA Gabb (p. 172). 
FIG. 1. View of Mr. Gabb’s type specimen frou: the collection of the Acad. Nat. Sci., Phila. 
1,2. Two views of a specimen which has lost the beak. Am. Mus. Nat. Hist., New York City. 
VOLUTODERMA ABBOTTI Gabb (p. 173). 
4,5. Views of the opposite sides of the type specimen from the Acad. Nat. Sci., Phila. 
6,7. Two views of a specimen from the Am. Mus. Nat. Hist., New York City. 
8,9. Similar views of a specimen from the Acad. Nat, Sci., Phila. 
LuNATIA HALLI Gabb (p. 175). 
10, 11. Views of the opposite sides of a specimen from Timber Creek, New Jersey, in the collec 
tion of the Am. Mus. Nat. Hist., New York City. 
NATICA ABYSSINA Morton (p. 175). 
12,13. Front and vertical views of a specimen from Timber Creek, New Jersey, in the collec 
tion of the Am. Mus, Nat. Hist., New York City, 
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