400 REPORT ON THE STATE CABINET. 



CEPHALOPODA. 



GENUS NAUTILUS, Breyn. 

 Nautilus occidentalis, Hall. 



Cyrtoceras giganteum, McCnESNEr. Descrip. New Palaeozoic Fossils, p. 67. Jan., 1860. 

 Lituites occidentalis, Hall. Rep. Prog. Geol. Survey Wisconsin for 1859, p. 31. Feb., 1860. 

 Lituites cancellatum, McChesnet. Descrip. New Palaeozoic Fossils, p. 96. 1861. 

 Nautilus (^Lituites') occidentalis. Hall. Geological Pieport of AVisconsin, p. 441. 1862. 



Shell very large, subdiscoidal. Volutions two or more, rapidly expand- 

 ing, contiguous, the outer portion of the last volution becoming fi'ee 

 and extending in a nearly straight line, while the earlier portions 

 are compressed on the ventral side by the dorsum of the preceding 

 volution; septa distant; section ellipitical; siphuncle small, sub- 

 central. Surface marked by regular equal fillet-like strias or ridges, 

 which are curved backwards on the dorsum ; and in more perfect 

 individuals, these are cancellated by finer longitudinal or revolving 

 striae. 



Specimens sometimes measure twelve inches in the greatest diameter 

 of the disc. 



This fossil was published by me, under the name occidentalis, in 1860. 

 The name giganteum, given by M'Chesnet, being preoccupied, the name 

 cancellatum was given a year later by that author. It appears to me that 

 these forms are not true Lituites, and that they should be referred to the 

 Genus Nautilus ; therefore since there is already a Nautilus giganteus, 

 the name occidentalis has precedence of cancellatus. 



Formation and Locality. — In limestone of the age of the Niagara group, 

 near Milwaukee, Wisconsin, and at Joliet, Illinois. 



Nautilus capax, Hall. 



Lituites capax, Hall. Report of Progress Geol. Survey Wisconsin for 1859, p. 3. 1860. 



This species differs from N. occidentalis in its more rotund form, the 

 section of the outer volution being very broadly elliptical or nearly cir- 

 cular, and showing rapid expansion toAvards the aperture. 



The materials possessed by me are friigmentary, but sufficient to leave 

 no doubt of specific distinction between it and the preceding species. 



