GENUS LITUITES. 363 



NAUTILUS OCCIDENTALIS. 



Cyrtoceras giganteurn : M'Chesney, Descriptions of Ne\vPala3ozoic Fossils, p. 67. 



Jan. 18G0'. 

 Lituites occfdcntalU : Hall, Report of Progress, Geol. Survey of Wisconsin for 1859, 



published Feb. 1860. 

 Lituites cancellatum : M'C. Loc cit. p. 96, 1861. 



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

 ing, contiguous, the outer portion of the last volution becoming free and 

 extending in a nearly straight line, while the earlier portions are com- 

 pressed on the ventral side by the dorsum of the preceding volution. 

 Septa distant. Section elliptical. Siphuncle small, subcentral. 

 Surface marked by regular equal fillet-like striae or ridges, which are 

 curved backwards on the dorsum ; and in more perfect individuals, these 

 are cancellated by finer longitudinal or revolving stria3. 

 This species sometimes measures twelve inches in the greatest diameter 

 of the disc. 



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

 The name giganteurn, given by M'Chesney, being preoccupied, the name 

 cancellatum was given a year later (1861) 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 accident alis has precedence of canceilatus. 



Formation and locality. In limestone of Niagara age, near Milwaukee, 

 Wisconsin, and at Joliet, Illinois. 



NAUTILUS CAPAX. 



Lituites capax : Hall, Report of Progress, Geol. Survey of "Wisconsin, 1859. Pub. 

 1860. 



This species differs from N. occide^itale in its more rotund form, the 

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

 lar, and showing rapid expansion towards the aperture. 



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

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



Formation and locality. In limestone of Niagara age, at Waukesha and 

 Racine, Wisconsin. 



PHRAGMOCERAS NESTOR. 



Page 43, original paper ; p. 338 of present Report. 



This species should be compared with P. ventricosum and P. arcuatum, 

 MuRCHisoN, Silurian System and Siluria. 



