PLATE LVIII. 



PAGE. 



Figs. 1 to 3a ONCOCERAS I.YCUM Hall 799 



1, 2, 3 Views of the body-chamber and a few air-chambers; showing the form of the 



aperture and contraction of the conch. 

 3a Outline of the septa. From the Trenton limestone, Minneapolis. 



Figs. 4 to 60 ONCOCERAS PANDION Hall 799 



4 Side view of an internal cast retaining the body-chamber and its apertural edge. 

 5, 6 Ventral and lateral views, showing the course of the septa. 



6a Outline of the septa, showing the ventral position of the sipho. Janesville, Wis. 



Figs. 7 to 9 ONCOCERAS CARVERI, sp. nov 799 



Dorsal, lateral and ventral views of an internal cast; showing the lateral com- 

 pression of the conch, the slight constriction of the body-chamber and the form 

 of the aperture. Trenton limestone, Minneapolis, Minn. 



Figs. 10 and II ONCOCERAS EXIGUUM Billings 798 



Two imperfect internal casts. From the Galena horizon at Fountain, Minn. 



Figs. 12 to 15a CYRTOCEKAS FEATHERSTONHAUGHI, sp. nov 807 



12, 13, 14, 15 Lateral, dorsal and ventral views; showing the characters of the species. 



15a Outline of a septum; showing the ventral position of the sipho. Cannon Falls, 

 Minnesota. 



Figs. 16 to 18b ONCOCERAS MINNESOTENSB, sp. nov 798 



16, 17, 18 Dorsal, ventral and lateral views of a specimen leading to the body-chamber; 



showing the longitudinal ridges of the surface. 



18a, 186 Outlines of septa, showing the ventral position of the sipho. From the Galena 

 beds at Lime City. Minn. 



