112 PROCEEDINGS OF THE NATIONAL MUSEUM vol.78 



Plate 4 



All illustrations, X 4, and the specimens from the Bright Angel shale, Middle 

 Cambrian, Grand Canyon, Ariz., except Figures 14-16. 



Page 



Figures 1, 2. Walcottella apicalis, new genus and species (genotype) 33 



1. Left valve. The large median tubercle is imperfect 



and the test somewhat exfoliated, but the outline 

 and other features characterizing the species are 

 clearly shown. (1, Chuar Valley; 2, Bass Can- 

 yon.) 



2. Broken right valve, the antero-dorsal half shown in 



figure almost perfectly preserved. The flattened 

 border of this valve is more distinct on the speci- 

 men than in the photograph. 

 3, 4. Walcottella concentrica, new species 34 



3. A large right (?) valve, the outline somewliat imper- 



fect on the right side. The concentric pitting of 

 the surface is well shown. 



4. A smaller, exfoliated valve, the surface markings 



being represented in this condition by minute 

 interrupted concentric wrinkles. (3 Bass Canyon; 

 4, Chuar Valley.) 

 5,6. Walcottella brevivs cilia, new species 3t 



5. A left valve preserving the comparatively coarse, re- 



ticular surface ornament. According to the 

 adopted orientation the median tubercle is behind 

 the middle of the valve in this species. 



6. Right valve, somewhat crushed, the ventral part of 



outline less convex than in fig. 5. (5, 6, Bass 

 Canyon.) 



7. Walcottella scitula, new species 35 



Tlie unique specimen on which this species is founded. 

 The ventral and posterior parts of the margin being 

 imperfect, the supposed original form is restored in 

 outline across the ground mass. 



8. Walcottella leper ditoides, new species 37 



The partially exfoliated but otherwise good left valve 

 upon which the species is based. As usual the surface 

 is very finely punctate or reticulate. The obsoles- 

 cense of the median tubercle emphasizes the resem- 

 blance and possible relations to Leperditia suggested 

 by the general form of the valve. (Bass Canyon.) 



