TRILOBITA—OPISTHOPARIA. 



279 



cheeks nearly as wide as the fixed cheeks and with genal spines. 

 Upper Cambric and Ordovicic. 



61. P. miniscaensis Owen. (Fig. 1578.) Cambric. 

 Glabella very strongly arched and tapering, eyes small. (Type 



of genus.) 



Upper Cambric, Potsdam (St. Croix) of Wisconsin. 



XXVI. Chariocephalus Hall. 



Differs from Ptychaspis in its broader and shorter cephalon, in 

 its large eyes situated near the anterior portion of the glabella, in 

 the different facial sutures, the wide free cheeks, and the divergent 

 genal spines. Upper Cambric. 



62. C. whitfieldi Hall. (Fig. 1579.) Cambric. 

 Fixed cheeks narrow, suddenly contracted in front of the eyes. 

 Upper Cambric, Potsdam (St. Croix) of Wisconsin. 



Fig. 1579. Chariocephalus whitfieldi. 

 (After Hall.) 



Fig. 1580. Parabolina spinulosa, 

 cephalon with free cheek, and pygidium 

 (c). (After Matthew.) 



XXVn. Parabolina Salter. 



Cephalon bordered by a marginal fold. Glabella of approxi- 

 mately the same width throughout. Ocular ridges prominent. 

 Eyes small, anterior. Genal spines present. Thorax with 12 

 segments ; axis narrow ; pleura with sharply pointed extremities, 

 bent backwards. Pygidium moderately small, with a lobed or 

 spinose margin. Cambric. 



63. P. spinulosa (Wahlenberg). (Fig. 1580.) Cambric. 



Free cheeks and area in front of glabella ornamented by raised 

 lines. 



Upper Cambric (Bretonian) of New Brunswick. 



