NIAGARA LIMESTONE OF CHICAGO, ILLINOIS. 113 



Fig. 15. — Coxocardium ORXATUM TV. and M Ill 



Fir;. 1 6. — Plattceras compl anatum W. and M 98 



16a. View of upper side. 



16b. View of aperture. 



Fig. 17. — Holopea niagarensis TV. and M 99 



Fig. 18. — Holopea chicagoexsis W. and M 99 



Fig. 19. — Subulites brevis TV. and M 99 



Explanation of Plate III. 



Fig. 1. — Pterinea subalata (Hall) TV. and M 109 



Cast showing linear posterior and anterior teeth. 

 Fig. 2.— Pterinea cxdata (Hall) TV. and M 109 



Cast showing linear posterior teeth. 

 Fig. 3. — Clidophorus mc chesxeyaxcs TV. and M 96 



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

 Fig. 4. — Pleurotojiaria gonopleura TV. and M 97 



Exterior of specimen with a defective base. 

 Fiff. 5. — Pleurotomaria sigaretoides TV. and M 98 



o 



Cast, defective at the aperture. 

 Fig. 6. — Porcellia senex TV. and M Ill 



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



6J. Dorsum of same, showing notch and nodular elevations. 

 Fig. 7. — Bellerophox (Tremaxotus) perforatus TV. and M 100 



7a. Cast, with apex and a portion of aperture broken away. 



7b. Portion of exterior of a specimen from near the aperture. 

 Fig. 8. — Gomphoceras MARCTiE TV. and M 101 



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. 



8c. Fragment, showing the obliquely moniliform sub-ventral siphon, and the convexity of the septa. 

 Fig. 9. — Lituites Hercules TV. 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 TV. and M 102 



10a. Cast of a cephalic shield. 



10J. Side view of the same. 



10c. Exterior of a defective pygidium. 

 Fig. 11. — Lichas decipiexs TV. and M 103 



Cast of a pygidium. 

 Fig. 12. — Bronteus occasus TV. and M 1 < >4 



Cast of pygidium. 

 Fig. 13. — Acidaspis Ida TV. and M 105 



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



MEM0IR9 BOST. SOC. NAT. HIST. VOL. I. 29 



