41 



mens the inner volutions are not disclosed. The surface of the 

 shell is covered with numerous, sharp, elevated, revolving lines, 

 separated by wider revolving furrows. 



Iq describing this species originally the other side of the volu- 

 tions was called the dorsal side of the shell, following the termin- 

 ology of Meek and most of the early authors; but Owen long 

 since showed that in the living Nautilus, the ventral side of the 

 animal is upon the outside and the dorsal side on the inner side 

 of the volution, and most late authors have made their descrip- 

 tions of the shells of Cephalopods conform to the position of the 

 animal in the shell of the Nautilus. We have adopted this method, 

 and the reader, in order to make comparison with the description 

 by Meek of coiled Cephalopods in the Geological Survey of Illi- 

 nois, and by other authors in North American Geology and Pal- 

 aeontology, and elsewhere, will find it necessary to reverse the 

 words dorsal and ventral as applied to the shells, so that they 

 may apply to the supposed position of the animal when within 

 the shell, as evidenced by the position of the Nautilus. 



The specimen here illustrated was found by Geo. K. Greene, at 

 the typical locality, in the St. Louis Group, at Crab Orchard, 

 Kentucky, and is now in the collection of Wm. F. E. Gurley. 



GONIATITES LUNATUS, n. sp. 



Plate V, Fig. 2, lateral view; Fig. 3, end of a volution and 

 ventral view, showing the surface markings on the shell; 

 Fig. 4, surface form of a septum taken from 

 thinner and smaller specimens; Fig 5, 

 end and ventral view of same. 



Species large, globose, volutions rather rapidly enlarging and 

 the periphery becoming more and more broadly rounded with the 

 growth of the shell. Figure 2 is a lateral view of a large speci- 

 men, though incomplete. It preserves part of the outer shell and 

 does not expose the septa. Figure 3 is a smaller specimen, show- 

 ing the outer shell but none of the septa. Figure 4 represents a 

 septum from a still smaller specimen, a ventral view of which is 

 represented by figure 5. Number of volutions not known. A 

 transverse section of a volution is lunate or crescentiform. The 

 last volution embraces all the inner ones and closes the umbilicus. 

 The air chambers are short and some parts of the septa come 

 very close together. 

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