TRILOBITA—OPISTHOPARIA. 3 1 1 



143. D. decipiens Winchell and Marcy. (Fig. 1621, f,g.) Siluric. 



Genal spines strong, flattened. Axis of pygidium strongly con- 

 vex anteriorly, tapering to a point posteriorly. 



Niagaran of Illinois and Wisconsin. 



LVI. Metopolichas Giirich. 



Cephalon tuberculate. Glabella broadly subtriangular, with a 

 broad median lobe, a pair of broad anterolaterals and postero- 

 laterals, and posteromedially from these, within the neck furrow, 

 a pair of small occipital lobes. Free cheeks broad, produced lat- 

 erally into broad genal spines curving outward and backward. 

 Pygidium broad; axis moderately short, of two rings; side lobes 

 broad, with three pairs of grooved segments, the two anterior 

 ending in free points. Siluric. 



iz^. M. breviceps (Hall). Siluric. 



Neck ring broad and flat. Pygidium semioval, longer than 

 wide; its axis forming a little more than one third its entire width. 



Niagaran of Ohio and Indiana. 



LVII. AciDASPis Murchison. 



Dorsal shield spinose; genal angles spiniform; margin of ceph- 

 alon thickened and spinose. Glabella with a large median and 

 two lateral lobes. Eyes small. Free cheeks large; facial sutures 

 extend from just within the genal angles inward to the eyes and 

 then forward, cutting the anterior margin on each side of the 

 glabella. Occipital spine present. Thorax of eight or nine seg- 

 ments, with ridged pleura extended into hollow spines. Pygidium 

 usually small, with spinose margin. Ordovicic-Devonic. 



145. A. quinquespinosa Salter-Lake. (Fig. 1621, /i.) Siluric. 



Cephalon nearly straight in front ; surface tuberculate. A straight 

 ocular ridge runs from the eye to the anterior edge of the gla- 

 bella. The portion of the fixed cheeks between the eye and the 

 glabella is swollen. Axial part of neck ring broad, with five spines 

 posteriorly. 



Niagaran of Arkansas. 



