684 CRETACEOUS PALEONTOLOGY. 



1868. Gyrodes Abbottii Con., Cook's Geol. N. J., p. 729. 



1876. Gyrodes abyssinis Gabb, Proc. Acad. Nat. Sci. PhiL 



(1876), p. 295. 

 1892. Natica abyssina Whitf., Pal. N. J., vol. 2 (Monog. U. S. 



G. S., vol. 18), p. 123, pi. 15, figs. 9-12. 

 1892. Gyrodes Abbottii Whitf., Pal. N. J., vol. 2 (Monog. U. 



S. G. S., vol. 18), p. 124, pi. 15, fig. 17. 

 1905. Natica abyssina Johns., Proc. Acad. Nat. Sci. Phil. 



(1905), p. 21. 

 1905. Gyrodes abbottii Johns., Proc. Acad. Nat. Sci. Phil. 



(1905), p. 21. 



Description. "Shell large, globose, with a flattened spire, the 

 inner volutions of which scarcely rise above the outer ones, and 

 are only two and a half to three in number ; volutions rather 

 ventricose and erect, ovate in a transverse section ; umbilicus large 

 and open to near the apex of the shell ; aperture ovate, two-thirds 

 as wide as long, and a little more convex on the outside than on 

 the inner margin, nearly equally rounded above and below ; suture 

 well marked and deeply impressed." (Whitfield.) The dimen- 

 sions of a large individual are : height, 57 mm. ; greatest diameter, 

 63 mm. ; height of aperture, 45 mm. ; width of aperture, 36 mm. 



Remarks. This species strongly resembles Gyrodes crenata 

 in general form, but, as the two species occur in New Jersey, it is 

 usually larger than that species. The casts of the two species can 

 be easily distinguished, however, by the contour of the lower side 

 of the volutions on the edge of the wide umbilicus, this portion 

 of the shell in N. abyssina being rounded, while in G. crenata it 

 is more or less angular or subcarinate. In the recent collections 

 of the Survey the two species have been observed, in general, to 

 be characteristic of different geologic horizons, N. abyssina 

 usually being a Navesink species, while G. crenata has not been 

 observed in that formation, being most commonly found in the 

 Merchantville clay-marl. In the collections of the National 

 Museum at Washington this species occurs abundantly from 

 Texas, with the shell more or less perfectly preserved. These 

 specimens show that the suture is canaliculate, the groove being 

 narrow and of moderate depth, with a sharp, subcarinate margin. 



