EXPLANATION OF PLATE III 

 Figures la to 5 are enlarged four diameters except Id which is enlarged eight diameters. 



Figs. la-Id. Yvania gurleyi ( Meek) p. 20 



la-d. The holotype. 



Id. Immature portion of the spire showing development (x8). 



Figs. 2-3b. Yvania inclixata Weller, n. sp p. 15 



2. A paratype. 

 3a-b. The holotype. 



Fig. 4. Yvania adamsi (Worthen) p. 30 



Internal cast from Peoria County. 



Fig. 5. Yvania giffordi (Worthen) p. 36 



Internal cast from Peoria County. 



The following curves indicate in a diagrammatic fashion the form of the apertures 

 of several of the species described. The whorl is to be considered as flattened out with 

 the suture above and the columella or umbilicus below. The horizontal mark midway 

 on the curves indicates the position of the angulation separating the lateral and basal 

 surfaces. It is to be noted that the apertures are broken away in all specimens observed 

 and therefore the depth of the slit is unknown. It probably does not exceed one eighth 

 of a turn. The relations of the aperture above and below the slit are also uncertain. 

 The curves presented herewith have been drawn from growth lines which left the slit 

 band opposite each other, although it is possible that the aperture was actually more 

 advanced upon one side than upon the other. 



Fig. 6. Yvania inclinata Weller, n. sp p. 15 



Fig. 7. Yvania gurleyi (Meek) p. 20 



Fig. 8. Yvania supercrexata Weller, n. sp p. 22 



Fig. 9. Yvania knigiiti Weller, n. sp p. 25 



F g. 10. Yvania subconstricta (Meek and Worthen ) p. 32 



Fig. 11. Yvania cifform (Worthen) p. 36 



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