49 



The aperture is compressed subelliptical, in outline, in the speci- 

 men illustrated, by fig. 9, with a moderately deep sinus al the angu- 

 lar back of the body whorl. And the shell substance is thin, which 

 indicates, probably, a young shell, or, it may be, the apical end of a 

 mature specimen. 



Fig. 10 represents a mature specimen. It is much extended upon 

 the back of the body whorl and the shed gradually becomes thicker, 

 but the aperture below the beak remains in the same position that 

 it is in in the specimen shown in fig. 8. The aperture increases its 

 length, and by reason of the lateral expansion of the shell with the 

 growth, it retains a compressed subelliptical outline, but acquires a 

 deep sharply angular sinus at the back of the shell. 



The surface is marked by concentric undulating strhe. that be- 

 come more and more pronounced toward the aperture. They are 

 not shown in the illustrations. 



This species is distinguished by the compressed angular serrated 

 back of the shell, and by the compressed, subelliptical aperture hav- 

 ing a deep, angular sinus. 



Platyceras thetts var. subspinosum, as illustrated in Pal. N. Y., 

 Vol. V, part 2, Plate III, fig. 30, has a continuation of the shell, 

 showing the older growth, similar to that preserved in our specimens 

 of this species, but the growth is not wholly upon the back of the 

 shell as it appears to be in this species. There is a great difference 

 in the growth of the shell, below the apex, in different species, and 

 in all species the apertures must change more or less With the 

 growth of the shell. 



Found by G. K. Greene near Charlestown, Indiana, in the Hamil- 

 ton Group, and now in the collection of Wm. F. E. Gurley. 



CLASS CEPHALOPODA. 

 Subclass TETRABRANCHIATA. 

 Order NAUTILOIDEA. 

 Family MELONOCERATID.E. 



REMELECERAS CLARKENSE n. sp. 



Plate IV, Fig. 1, lateral view; Fig. 2, dorsal view; Fig. 3, ventral 

 view of the same fro g went. 



Prof. Hyatt founded the genus Remeleceras, dedicated to Remele, 

 an author on Cephalopods, in 1894, in the Proceedings of the Ameri- 

 —7 



