PLATE LX. 



PAGE. 



Figs. 1 to 4 CYRTOCERAS 8HUMARDI, sp. nov 



Dorsal, lateral, ventral and septal views of the typical specimen; showing its 

 robust form, broad venter, outline and convexity of septum and position of 

 sipho. Trenton limestone, Cannon Falls, Minn. 



Figs. 5 and 6 CYRTOCERAS CAMURUM Hall 805 



Lateral and ventral views of two fragments believed to belong together and 

 drawn as one. The lower portion shows the position of the sipho and the 

 narrowing of the conch is due to compression. 



Figs. 7 to 9 CYRTOCEKAS NORWOODI, sp. nov 809 



Lateral, ventral and dorsal views of a specimen showing the body-chamber, with 

 a number of very narrow air-chambers, the fine undulation of the sutures, 

 position of sipho, broad and obscure longitudinal bands and the almost impal- 

 pable incurvature of the conch. In the Trenton limestone at Eockton, Minn. 



Fig. 10 CYRTOCERAS BILLINGSI Sailer 806 



A portion of a shell showing the finely and sharply lineate exterior of the conch. 

 Trenton limestone, near Cannon Falls, Minn. 



Figs. 11 and 12 CYRTOCERAS HALLIANUM D'Orbigny 805 



Lateral views of a specimen, showing the undulating lamellae and some of the 

 septa. From the Trenton limestone at Janesville, Wisconsin. 



Figs. 13 to 15 ONCOCERAS DOUGLASSI, sp. nov 801 



Lateral, ventral and dorsal views; showing the rapidly expanding conch and the 

 contracted body-chamber. These figures are not wholly satisfactory, flg. 13 

 being slightly oblique in position and not affording an exact profile; the lower 

 septa in figs. 14 and 15 are too oblique. From the Galena beds at Holder, Minq. 



