GASTEKOPODA OP THE LOWER GREEIST MARLS. 125 



be perfectly smooth on the top, as in Dr. Morton's specimens. I have, 

 however, given it a distinct specific reference and place in the volume, 

 that, in case other specimens should be found, it may retain its individu- 

 ality as a species. 



Formation (Did locality: In coarse ferruginous sand of the Lower Marls, 

 at Mullica Hill, New Jersey. Collection Acad. Nat. Sci., Phila. 



'% 



Gyrodes infracarinata. 



Plate XV, Figs. 13-16. 



Natica'infracarinata Gabb : Proc. Acad. Nat. Sci., Pliila., 1861, p. 319. 

 Gyrodes-lnfracarinata (Gabb) Meek: GeoL, N. J., Newark, 1868, p. 739. 



Shell, as shown by internal casts, large, depressed globular above and 

 truncate below by the broad umbilical area shortening the depth of the 

 shell; spire consisting of about four volutions, the last one of which forms 

 fully two-thirds of the bulk of the entire shell; volutions oblique, largest 

 below the middle, slightly flattened on the top adjacent to the suture, and 

 very strongly angular on the base bordering the very wide open umbilicus, 

 in which the volutions are exposed nearly to the apex; aperture large, 

 ovate, widest below the middle and truncate at the upper angle by the flat- 

 tening of the volution adjacent to the suture; columellar lip apparently 

 quite thin, and marked by a single spiral thread-like ridge on its inner sur- 

 face; outer lip sharp and thin and very strongly receding below, as seen in 

 a. profile view; surface of the cast usually smooth, but sometimes showing 

 evidences of transverse strise of growth. 



The New Jersey specimens of this species are all internal casts, con- 

 sequently the surface features are unknown. The casts indicate a strong 

 roljust species, with rapidly increasing volutions, which are short in com- 

 parison to their lateral dimensions. The suture is very strongly marked, 

 showing considerable thickening of the shell at the junction of the volu- 

 tions. The features of the umbilicus are taken from specimens where the 

 filling of this part has been taken out of the cast and preserves the surface 

 markings, thereby giving the features in a perfectly reliable manner. The 

 examples seen from New Jersey are not as large as those of G. abyssintis 

 from the southern localities, but they are found having a diameter of nearly 



