Figs. land 2 
1 
2 
Fig. 3 
Fig. 4 
Figs. 5 to 7 
PLATE LVI. 
TRIPTOCERAS LAMBI Whiteaves 
View of a large specimen. 
One of the septa; showing the form of the shell in cross-section and the position 
of the sipho. From the Galena limestone, Stewartville, Minn. 
TRIPTOCERAS PLANOCONVEXUM Hall.........ccc ce cece cc neee cere eeetereercensecce 
(See also plate LVII.) 
View of an internal cast. 
Trenton limestone, Cannon Falls, Minn. 
TRIPTOCERAS PLANODORSATUM Whitfleld.........--sceece cece cree cece ee eee sees 
(See also plate LYM.) 
View of the flatter side of an internal cast; showing the curvature of the septa. 
Trenton limestone, Minneapolis. 
TRIPTOCERAS OWENI, SP. DOV .....--- see e ese e eet e nsec eee e ence eset ecee ce ceeetscees 
Three views of the typical specimen, showing the contour of its surfaces. 
Trenton limestone, Cannon Falls. 
