GENUS CYRTOCERAS. 349 



This species differs from the P. hector (Billings) of the Guelph lime- 

 stone of Canada, in being more narrowly elliptical in section, and much 

 more expanded in the dorso-ventral direction at the aperture, as well as in 

 the greater length and more extreme constriction of the intermediate por- 

 tion of the aperture. 



Formation and locality. In the limestone of the Niagara group, at 

 Wauwatosa, Wisconsin. 



GENUS CYRTOCERAS (Goldfuss). 



CYRTOCERAS LUCILLUS (n. s.). 



Shell arcuate, gradually expanding towards the aperture, section elliptical, 

 a little narrower on the inner side of the curve ; septa moderately con- 

 vex, closely arranged ; siphuncle small, submarginal on the outer side 

 of the arch. 

 Surface marked by regular equal neatly defined annulations, which have 

 a slight retral arch on the exterior curve, indicating a similar sinuosity 

 in the margin of the aperture. The annulations are closely arranged : on 

 the smaller parts of the shell, they are in the proportion of twenty in 

 the space of an inch ; while on the inner side of the curve they are more 

 approximate, and on the outer side more distant. On the larger part of the 

 shell, the annulations number five or six in the space occupied by seven in 

 the smaller parts. 



Formation and locality. In limestone of the Niagara group near Wau- 

 watosa, Wisconsin. 



CYRTOCERAS FOSTERI. 



Cyrtoceras fosteri : Hall, Report of Progress Geol. Sur. of Wisconsin, 1860-61, p. 41. 

 This species is known to me only in the Niagara limestone near Chicago. 



CYRTOCERAS DARDANUS. 



Cyrtoceras dardanus : Report of Progress Geol. Survey of Wisconsin, 1860-1, p. 43. 



This species was originally described from fragments, which in all the 

 specimens seen can be readily identified. Some other imperfect specimens 

 which have come under my notice since the publication of the original 

 description, have induced me to suppose that the fossil may belong more 

 properly to the Genus Gyroceras. The species occurs at Waukesha and 

 Wauwatosa, Wisconsin. 



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