EXPLANATION OF PLATE XXIII. 



Figures 1-2 CERATOCEPHALA GONIATA Warder p. 255 



Anterior and lateral views of a nearly complete cephalon,from 

 Hawthorn (Pal. Coll. Walker Museum, No. 9,885, Van 

 Home Collection.) 



Figures 3-4 ACIDASPIS VANHORNEI n. sp p. 251 



Dorsal and lateral views of the type specimen, from Bridge- 

 port. (Pal. Coll. Walker Museum, No. 9,886, Van Home Col- 

 lection.) 



Figures 5-6 ODONTOPLEURA ILLINOIENSIS n. sp p. 253 



5, Dorsal view of an incomplete cranidium. 6, Dorsal view of 

 a nearly complete pygidium. Both specimens from near 

 Joliet. (Pal. Coll. Walker Museum, No. 10,745.) 



Figures 7-8 ARCTINURUS CHICAGOENSIS n. sp p. 248 



7, Dorsal view of an incomplete cranidium. 8, Dorsal view of 

 an incomplete pygidmm restored in outline. Both speci- 

 mens from Hawthorn. (Pal. Coll. Walker Museum, No. 

 9,860, Van Home Collection.) 



Figures 9-10 GALYMENE NIAGARENSIS Hall p. 261 



Lateral and dorsal views of a nearly complete individual, from 

 near Lemont. (Pal. Coll. Walker Museum, No. 10,746.) 



