PLATE LIV. 



PAGE. 



FigS. 1 tO 3 ACTINOCERAS REMOTI8EPTUM Hall 782 



1 Outline of a large example. 



2 The form of the transverse section. 



3 The first two air-chambers, longitudinally sectioned: showing the bulbs of the 



sipho, their thickened walls and endosiphon with its ramifying branches. 

 xl 1-6. From the Trenton limestone at Cannon Falls, Minn. 



Figs. 4 and 5 OBTHOCERAS FERROTI, sp. nov 785 



4 A view of a silicifled shell, showing the closely annulated exterior and the strong 



alternating vertical strise. 



5 Transverse section at the terminal septum. 



Figs. 6 and 7 ORTHOCERAS BILINEATUM Hall 786 



(See also plate XLVH.) 



6 View of an internal cast showing the relations of annulations and septa. 



7 Another specimen illustrating the same features. 



From the Trenton shales at Minneapolis. 



