TRILOBITA—OPISTHOPARIA. 277 



more elevated in the middle. Anterior furrows very short, pit- 

 like. Occipital ring with a small, short, tubercle-like spine di- 

 rected slightly backwards. 



Middle Cambric of St. John group (Acadian) of New Brunswick. 



54. P. ouangondiana Hartt. (Fig. 1576, J, ^.) Cambric. 

 Cephalon narrowly rounded ; anterior margin wide, with a strong 



fold, its width less than the length of the entire cephalon. Gla- 

 bella long, very convex. Middle of occipital ring with a short 

 spine. Neck furrow conspicuous. Surface smooth. 



Middle Cambric of St. John group (Acadian) of New Brunswick. 



55. P. oweni Meek and Hayden. Cambric and Ordovicic. 

 Free cheeks narrow. Glabella very convex, wide and long. 



Eyes short, arched. Frontal rim strongly rounded. 



Upper Cambric of South Dakota; Middle (?) and Upper Cam- 

 bric of Montana, etc. ; Upper Cambric and Lower Ordovicic of 

 Nevada. 



56. P. (Lonchocephalus) wisconsinensis (Owen). Cambric. 

 Frontal limb very broad, occipital spine long and curving. 



Flat Head formation of Yellowstone region ; St. Croix of Min- 

 nesota and Wisconsin. 



XXII. SoLENOPLEURA Angclin. 

 Cephalon wide, semicircular. Glabella prominent. Dorsal fur- 

 rows deep. Fixed cheeks almost as high as the glabella. Frontal 

 limb convex. Neck ring with a tubercle. Genal angles pointed. 

 Thorax with 14 segments; ends of pleura bluntly rounded. 

 Pygidium rather small, with few united segments. Surface of 

 test granulose or tuberculate. Cambric. 



57. S. acadica Whiteaves. (Fig. 1577.) Cambric. 

 A furrow bounds the inner side of the marginal rim. Surface 



of glabella finely granulose. 



Middle Cambric of St. John group (Acadian) of New Brunswick. 



58. S. jerseyensis Weller. Cambric. 

 Glabella with two pairs of furrows, the anterior pair very faint 



and transverse, the posterior stronger and arched backward. The 

 entire glabella tapers backward into a very broad triangular spine; 

 neck furrow deep, causing a slight separation of the spine and the 

 glabella. 



