NIAGARA LIMESTONE OF CHICAGO, ILLINOIS. 113 



Fig. 15. CONOCAKDIUM ORNATUM W. and M ^ .<<.... Ill 



Fig. 16. PLATYCERAS COMPLANATDM W. and M 98 



16a. View of upper side. 



166. View of aperture. 



Fig. 17. HOLOPEA NIAGAKENSIS W. and M 99 



Fig. 18. HOLOPEA CHICAGOKNSIS W. and M 99 



Fig. 19. StJBULiTES BREVIS W. and M 99 



EXPLANATION OF PLATE III. 



Fig. 1. PTERINEA SUBALATA (Hall) W. and M 109 



Cast showing linear posterior and anterior teeth. 

 Fig. 2. PTERIKEA UNDATA (Hall) W. and M 109 



Cast showing linear posterior teeth. 

 Fig. 3. CLIDOPHORUS MC CHESNEYAKUS W. and M 96 



Cast of left valve showing clavicular impression, muscular scar and pallial outline. 

 Fig. 4. PLETTROTOMARIA GONOPLEURA W. and M 97 



Exterior of specimen witli a defective base. 

 Fig. 5. PLEUROTOMARIA SIGARETOIDES W. and M 98 



Cast, defective at the aperture. 

 Fig. 6. PORCELLIA SENEX W. and M Ill 



6a. View of aperture and spire of a cast. 



66. Dorsum of same, showing notch and nodular elevations. 

 Fig. 7. BELLEROPHON (TREMANOTXJS) PERFORATUS W. and M 100 



la. Cast, with apex and a portion of aperture broken away. 



76. Portion of exterior of a specimen from near the aperture. 

 Fig. 8. GOMPHOCERAS MARCYJE W. and M 10 1 



8a. Left side of a cast, showing the faint encircling furrows, and an outline continuation of the 

 specimen to near the apex, as demonstrated in specimens actually examined. 



86. View of the aperture of another specimen. 



Sc. Fragment, showing the obliquely moniliform sub-ventral siphon, and the convexity of the septa. 

 Fig. 9. LITUITES HERCULES W. and M 101 



Cast of a medium-sized specimen, drawn one half the natural size, showing chamber of habitation 

 with faint encircling furrows. 



This is not a representation of one of the typical specimens, and there is even some doubt of its 



specific identity with them. 

 Fig. 10. LICHAS PDGNAX W. and M ; 102 



10a. Cast of a cephalic shield. 



106. Side view of the same. 



lOc. Exterior of a defective pygidium. 

 Fig. 11. LICHAS DECIPIENS W. and M 103 



Cast of a pygidium. 

 Fig. 12. BRONTEUS OCCASUS W. and M 104 



Cast of pygidium. 

 Fig. 13. ACIDASPIS IDA W. and M 105 



Cast of cephalic shield, with spines restored, as seen in numerous specimens. 

 9 



