GASTEROPODA OP THE LOWEE GUEEN MARLS 127 



have a much bi'oader umbiUcus, and are more angular at the base of the volu- 

 tion. They correspond in nearly all particulars, as to form, with G. ahyssinus 

 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. Ahbotti Grabb 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. Abbotti 

 being a large shell. 



Formation and locality: In the micaceous clays below the Lower Marls 

 of the Cretaceous formation, at Haddonfield, New Jersey. 



Gyrodbs petrosus. 

 Plate XVI, Figs. 1-4. 



Natica petrosa Morton: Synop. Org. Rem. Cret., p. 48, PI. XIX, Fig. 6. 



Gyrodes petrosus (Mort.) Gabb : Synopsis, p. 61; Proo. Acad. Nat. Sci., Pliila., 



1876, p. 295; Meek, Check List Cret. and Jur. Foss., p. 21; Geol. K J., 



Newark, 1868, p. 729. 

 Gyrodes alveata (Conrad) Gabb: Proc. Nat. Sci., Phila., 1876, p. 295. 

 Natica alveata Conrad : Jour. Acad. Nat. Sci. , Pfiila. , 2d ser. , vol. 4, p. 289, PL 



XLVi, Fig. 45. 



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 

 greatest 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. 



