250 



TRILOBITA 



Fam. 12. Cheiruridae (Fig. 151, D, E).— The glabella is 



^ 



Fig. 151.— a, Phillipsia gemmulifera. Phill., Carboniferous. B, Arethusina konincki, 

 Barr., Ordovician. C, Dalmanites limulurus. Green, Silurian. (After Hall.) D, 

 Clieirurus insignis, Beyr., Silurian. E, Dcijyhon forhesi, Barr., Silurian. F, 

 Acidctspis dufroioyi, Barr., Silurian. (A, B, from Zittel ; D, E, F, after Barrande ; 

 natural size.) 



convex or inflated, and distinctly defined. The facial suture 

 passes from the lateral to the front margin. The free cheeks 



