170 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 64 



Facial sutures as shown by figures 2, 2a, 2b, plate 27. 



Thorax with 9 segments ; axial lobe convex, with a shallow 

 transverse furrow on each side that serves to define a small tubercle 

 next to the dorsal furrow; pleural lobes wide; a strong, straight 

 furrow extends from the inner end of each segment nearly to the 

 rounded end, which terminates irf a falcate point sloping obliquely 

 backward. A slender, long median spine (fig. 2/) occurs on 

 some of the axial lobes as in N. tenera (pi. 28, figs. 2d-e). 



Pygidium transverse; axial lobe divided into three rings and a 

 terminal section by shallow transverse furrows ; pleural lobes large 

 and marked by four gently backward-curving furrows ; border 

 narrow. 



The outer surface of the test appears to have been minutely 

 granulated, but as all the specimens are preserved in a fine argil- 

 laceous shale, the outer surface is so injured by compression when 

 the test was in a plastic condition that most of the irregularities, if 

 such existed, have become obscured. 



Dimensions. — One entire dorsal shield has a length of 11 mm. 

 Some cranidia indicate that others may have had a length of 13 

 to 15 mm. 



Observatioiis. — Fragments of this species are abundant in the 

 shale, but entire dorsal shields are rare. Figure 2, plate 27, has been 

 restored in part from several specimens, of which only one injured 

 example shows the entire cephalon, thorax, and pygidium. 



The cranidium of A'', gracilis dififers in so many details from the 

 other species that a comparison of the figures on plate 27 will enable 

 the student to readily distinguish them. 



Formation and locality. — Upper Cambrian: (90a, 91) Cona- 

 sauga shale; Cedar Blufif, (92X, 145) Yancey's Bend and east of 

 Turkeytown, all three on Coosa River; and (92XX) from brook on 

 road from Lydia Angles to Blaine, Center Township, all in Cherokee 

 County, Alabama. 



Upper Cambrian: (124) Nolichucky shales overlying limestone 

 which rests on the Rogersville shale, on Big Creek, southeast of- 

 Harlans Knob, 4 miles (6.4 km.) northeast of Rogersville, Hawkins 

 County; and (io6a) east of Shooks Ridge, in Bays Mountains, 10 

 miles (16.1 km.) southeast of Knoxville, Knox County, both in 

 Tennessee. 



Also Conasauga formation; (96c) shales 4 miles (6.4 km.) north- 

 west of Rome, Floyd County, Georgia; and (358e) Birmingham 

 City, Jefferson County, Alabama. 



