NO. 3 CAMBRIAN TRILOBITES 211 



The pygidia from Potatotop and Bartlett Hollow correspond to 

 the above description very closely, and also to the pygidia of the 

 Crepicephalus that I have identified as C. tcxanus from the Upper 

 Cambrian of Montana. 



By comparing the specimens that are of similar size from the 

 Cap Mountain limestone of Texas and the Conasauga shales of 

 Coosa River, Alabama, they appear to be identical. In both, the 

 glabella is broadly conical with frontal limb of medium width and 

 separated from the frontal rim by a strong rounded furrow marked 

 by three slightly transverse pits. In both, the outer surface of the 

 glabella is nearly smooth or marked by low, scattered tubercles, 

 while the fixed cheeks, frontal limb and rim are marked by rather 

 strong granulations or tubercles. There is also a slight node near 

 the center of the well-defined occipital ring ; at each locality we find 

 the long and shorter glabella, narrow rounded, intermediate and 

 wide flattened frontal rim. As the cranidia increase in size, the 

 frontal rim broadens so as to be proportionately wider than the 

 frontal limb. 



The following is a description based upon the Alabama speci- 

 mens : General form of dorsal shield broadly oval ; axial lobe con- 

 vex, about half as wide as the pleural lobe. Cephalon broad, trans- 

 versely semicircular, with a well-defined border that varies in width 

 from narrow in young subjects to quite broad in the older individuals. 

 Cranidium with strong, broadly conical glabella that is marked by 

 three pairs of short lateral furrows ; occipital ring of medium width 

 and marked at its center by a small sharp-pointed node ; occipital 

 furrow broad, rounded, and narrowing at each end ; dorsal furrow 

 about the glabella deeply impressed. Fixed cheeks relatively narrow 

 and generally convex ; palpebral lobes rather large and nearly equal 

 to one-third the length of the cranidium on the line of the facial 

 suture ; the narrow fixed cheeks merge into the relatively strong 

 frontal limb, which is slightly convex and sloping downward to a 

 well-defined transverse furrow, which is marked by three more or 

 less strong, slightly transverse pits, the center one of which is on 

 the line of the axis of the glabella and the lateral ones are on a Hue 

 with the sides of the glabella near its posterior margin ; frontal 

 border varying from a narrow, slightly convex border in young 

 specimens to a broad flattened border in the older and larger indi- 

 viduals ; postero-lateral limbs long, rather narrow, and marked by a 

 well-defined intramarginal furrow. The free cheeks terminate at 

 the genal angles in rather strong, backward-extending spines. 



