686 CRETACEOUS PALEONTOLOGY. 



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



(1905), p. 21. 

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



(1905), p. 21. 



Description. Shell of medium size, the dimensions of a rather 

 large internal cast being: maximum width, 30 mm., height, 23 

 mm.; height of aperture, 20 mm.; width of aperture, 13.5. 

 Depressed globular above with a depressed spire, broadly umbm- 

 ,cate below. Volutions about four in number, the outer one of 

 which forms fully two-thirds of the bulk of the entire shell, 

 largest below the middle, the casts slightly flattened on top adja- 

 cent to the suture, strongly angular on the base bordering the 

 umbilicus. Aperture large, oblique; widest below the middle. In 

 specimens preserving the shell, or in impressions of the exterior, 

 a distinct band of elevated crenulations or transverse nodes marks 

 the top of the volutions just below the suture, and forms a 

 decided ridge around the spiral portion of the shell. Surface of 

 the shell marked by fine lines of growth parallel with the margin 

 of the aperture, and passing over the line of nodes on the upper 

 surface of the volution. 



Remarks. Casts of this species in the Merchantville clay-marl 

 are sometimes modified by the compression of the matrix so as 

 to preserve most of the external features of the shell. The upper 

 portion of the volutions is distinctly flattened so as to form a dis- 

 tinct revolving angulation at a little distance from the suture, 

 but the crenulations are not often seen on these modified casts. 

 The shell surface is marked by distinct transverse lines of 

 growth, which are directed rather strongly backward below the 

 revolving angulation, so that the outer lip of the aperture is 

 strongly oblique in lateral view. The casts resemble those of 

 Gyrodes dbyssina, but in the New Jersey collections they are 

 always smaller than the larger individuals of that species, and 

 they may be distinguished by the angular or subcarinate margin 

 of the broad umbilicus, which is notable even in the casts. The 

 two species also have a different geologic range in the New Jer- 

 sey beds. In the southern localities the species often grows to a 

 larger size than any of the specimens observed in New Jersey. 



