114 PROCEEDINGS OF THE NATIONAL MUSEUM vol.78 



Plate 5 



Unless otherwise stated all figures X 4, and specimens from the Middle Cam- 

 brian, Bright Angel shale of the Grand Canyon, Ariz. 



Page 



Figures 1-3. Walcottella limatula, new species 40 



1. A right valve showing surface ornament very dis- 



tinctly. The specimen is more elongate than 

 usual, but this difference is partly accounted for 

 by the removal of the ventral part of the fiat rim. 



2. Left side of a nearl}^ perfect carapace — the holotype 



of the species. The specimen retains the surface 

 ornament and shows the small "ocular node" and 

 the larger median tubercle very satisfactorily. 

 The anterior narrowing of the valves is character- 

 istic of the species. 



3. Ventral view of same showing anterior and posterior 



gaping of valves. 



4-5. Walcottella ventrosa, new species 41 



Light and dark prints of photograph of a nearly perfect 

 right valve. This species is closely allied to W. 

 limatula, but differs in its form, being relatively 

 shorter, more rounded and produced ventrally, and 

 narrower posteriorly. 



6. Walcottella subtruncata, new species 41 



A good photograph of a right valve of this species. 

 Except that its postdorsal part is somewhat abraded, 

 the specimen is perfect. The truncation of the ante- 

 rior side and the relatively short subovate, or sub- 

 quadrate, form distinguish the species from its 

 nearest congeners. 



7. Walcottella longula, new species 42 



A complete right valve. The photograph is not very 

 good, being fiat and lacking detail. However, it 

 shows the features chiefly relied on in defining the 

 species. In the shape and surface elevations of the 

 anterior half it is much like W. subtruncata, but the 

 valve on the whole is much longer and quite different 

 in form posteriorly. Surface punctate as in Figures 

 1 and 6. 



8. Walcottella oblonga, new species 38 



A right valve, well preserved except along the post- 

 ventral portion of the margin. As shown in the 

 figure the general form as preserved resembles that 

 of W. longula, but the medium tubercle is much less 

 prominent and the puncto-reticulata surface orna- 

 ment coarser. The original form of the specimen 

 was probably not greatly unlike that of Figure 15 on 

 this plate. The true affinities of W. oblonga are prob- 

 ably with W. scitula. 



