738 THE PALEONTOLOGY OF MINNESOTA. 



(Note on Ceraurus. 



We may summarize and tabulate the subgeneric relations of the best known 

 American representatives of Ceraurus, in the following manner: 



1. Pygidium with first pair of ribs much produced and embracing the short extension of the other 



one or two pairs. 



a. Glabella depressed, subquadrate; glabellar furrows short and horizontal: Ceraurus s. s. 



C. pleurexanthemus Green. 

 C. polydorus Billings. 

 C. pompilius Billings. 

 C. nuperus Billings. 

 C. tarquinius Billings. 



b. Glabella ovoid, convex; glabellar lobes posteriorly oblique, third lobe not separated; ocular 



ridge continuous with frontal border: Cyrtometopus. 

 C. apollo Billings. 

 C. mercurius Billings. 

 C. rams Walcott. 

 C. scofieldi Clarke. 



c. Glabella elliptical, convex behind, with obliquely posterior furrows; third lobes not separa- 



ted; usually a spine on the posterior portion of the glabella: Nieszkowskia. 

 C. glaums Billings. 

 C. perforator Billings. 

 C. satyrus Billings. 

 C. numitor Billings. 



d. Frontal and first and second lateral lobes confluent and highly convex or subspherieal: 



Sphccrocoryphe. 

 S. robusta Walcott. 

 S. salteri Billings. 



2. Pygidium with free pleural ribs not extending beyond the posterior arc. 



e. Glabella subquadratn, rounded and full in front; lateral furrows short and horizontal; 



third lobe not separated; pygidium with four pairs of broad obtuse marginal 

 extensions: Eccoptochile. 

 C. icarus (Billings) Meek. 



/. Glabella with large and convex frontal lobe; members of first and second lateral furrows 

 confluent; third lobes wholly isolated. Pygidium with six distant, sharp, 

 incurved caudal spines: Crotalocephalus. , 



C. niagarennis Hall ( C. insignis Beyrich.) 



g. Glabella convex, ovoid or subtriangular; frontal lobe small, lateral furrows oblique; third 

 lobe large and not isolated. PyKidium with eight divergent spines: Pseudo- 

 sphcerexochus. 

 C. proliflcus Billings. 

 P. trentonensis Clarke. 



