NO. 3 UPPER CAMBRIAN TRILOBITE FAUNAS RASETTI 67 



almost parallel to posterior cranidial margin, sharply curving back- 

 ward, cutting margin near base of genal spine. Genal spine slender, of 

 moderate length. Furrow on posterior area obsolete on outer surface, 

 impressed on interior cast. Free cheek completely lacking border fur- 

 row on outer surface, entirely convex, extended into a short, slender 

 strip that simulates a genal spine, but actually contributes to the 

 cephalic margin in a region in advance of the base of the genal spine 

 borne by the cranidium. Visual surface of eye convex, bean-shaped; 

 facets indistinguishable. 



Pygidium approximately semicircular, twice as wide as long. Facets 

 well developed. Posterior outline with uniform curvature. Axis well 

 defined anteriorly but merging with the pleural lobes posteriorly, 

 showing 2 rings plus a terminal indistinctly segmented section. Pleural 

 lobes entirely convex, lacking any furrows, showing barely a trace of 

 differentiated border. Surface of cranidium and free cheeks perfectly 

 smooth. Pleural lobes of pygidium with very fine, transverse terrace 

 lines only visible under conditions of perfect preservation. 



Discussion. — This species is quite distinctive in the lack of all 

 furrows on the outer surface, and especially the narrowing of the 

 cranidium in front of the eyes. The pygidium is much like Norwoodia 

 gracilis and N. rogersvillensis and unlike Norwoodella safjordi, N. 

 kingstonensis, and N. rotundicollis. This fact would perhaps justify 

 redistributing the species hitherto referred to Norwoodia and Nor- 

 woodella on the basis of the pygidia, rather than the questionable 

 character of the structure of the frontal area. This revision should only 

 be undertaken when the pygidia of most species of this group are 

 known with certainty. For the present species the assignment is cer- 

 tain, since only one species of the Norwoodiidae occurred in the beds 

 yielding the material illustrated herein. 



Occurrence. — Basal portion of the Nolichucky (Cedaria zone). 

 The type locality is U.S.N.M. 107a, NW. of Knoxville. The specimens 

 illustrated are from the collections cne/10, Comby Ridge (= U.S.G.S. 

 collection 2407), and cne/12 near Heiskell (the latter presumably 

 close to or identical with the type locality) . 



Types. — Holotype and paratypes: U.S.N.M. 94880. Plesiotypes: 

 U.S.N.M. 144616-8. 



NORWOODELLA HALLI Resser 



Plate 4, figures 8-15 



Norwoodella halli Resser, 1938a, p. 90, pi. 10, figs. 45, 46. 

 Norwoodella halli Resser, Lochman, 1940, p. 47, pi. 5, figs. 31-36. 



The types are cranidia preserved in shale. Lochman gave a detailed 

 description of the species and figured unflattened limestone material 



