Explanation of Plate VI. 



Drawings by Sydney Prentice, except No. 12, which is by C. McK. Beede. 

 All specimens natural size. 



Seminula argentia. Variation of spires. 



Fig. 1. Specimen brachial side up. 



Fig. 2. This specimen shows spires viewed with pedicle side partly removed. 



Fig. 3. Pedicle view, showing part of spire. 



Fig. 3c/. Above individual, brachial side up. 



Fig. 4. Brachial side of fig. 4a. 



Fig. 4a. Pedicle view of specimen, showing position of spires. 



Figs. 5 and 5a are the brachial and pedicle views of a Bomewhat laterally com- 

 pressed specimen. 



Fig. 6. Pedicle view of specimen. 



Fig. 6a. Brachial view of fig. 6. 



Figs. 7 and 7a are the brachial and pedicle views of a specimen. 



Fig. 8. This figure probably shows the brachial side of specimen, while fig. 8a 

 is the opposite side. 



Fig. 9. Brachial view. 



Fig. 10. The pedicle view of a specimen, and fig. 10a the brachial side of th& 

 same. 



Fig. 11. Brachial valve nearly ground away, to show spire. The sickle-shaped 

 structure is probably the base of the opposite spire. Beede's collec- 

 tion. 



Fig. 12. Specimen with brachial valve largely broken away. 



All specimens but No. 11 in collection of University of Kansas. 



