GASTEROPODA OF THE LOWER GREEN MARLS 127 
have a much broader umbilicus, and are more angular at the base of the volu- 
tion. They correspond in nearly all particulars, as to form, with G. abyssinus 
Morton’s sp., but have a broader truncation or flattening of the upper surface 
of the volution, are less erect in form, and differ in the crenulated sides of the 
upper surface. In this last feature they correspond very closely with what 
the young shell of G. Abbott? Gabb ought to be, and also in the form of the 
umbilicus and obliquity of the shell, and I am not sure that they are spe- 
cifically distinct, though the small number of individuals of each species 
which I have seen render it difficult to determine with certainty, G. Abbott 
being a large shell. 
Formation and locality: In the micaceous clays below the Lower Marls 
of the Cretaceous formation, at Haddonfield, New Jersey. 
GYRODES PETROSUS. 
Plate xvi, Figs. 1-4. 
Natica petrosa Morton: Synop. Org. Rem. Cret,, p. 48, Pl. xix, Fig. 6. 
Gyrodes petrosus (Mort.) Gabb: Synopsis, p. 61; Proc. Acad. Nat. Sci., Phila., 
1876, p. 295; Meek, Check List Cret. and Jur. Foss., p. 21; Geol. N. J., 
Newark, 1868, p. 729. 
Gyrodes alveata (Conrad) Gabb: Proce. Nat. Sci., Phila., 1876, p. 295. 
Natica alveata Conrad: Jour. Acad. Nat. Sci., -Phila., 2d ser., vol. 4, p. 289, PL. 
XLVI, Fig. 45. 7 
Shell (as seen in casts) of medium size or smaller, obliquely oval or 
depressed and somewhat patulose, with a low spire; the entire adult shell 
having three to three and a half volutions, the last of which forms the 
ereatest bulk of the shell; volutions obliquely compressed from above, 
largest below the middle, often slightly flattened on the upper half and with 
a distinct flattened space bordering the suture; aperture large, very oblique, 
strongly receding below as seen in profile on its edge; semilunate in out- 
line, rounded below and slightly acute above, somewhat modified in the 
upper part by the intrusion of the preceding volution; umbilicus large, 
broadly patulose within, and apparently without callus; peristome thin, 
and the substance of the shell also apparently slight; surface of the shell 
unknown. 
