PLATE I. 1 
RHYNCHONELLAS OF THE SQUARE LAKE LIMESTONE. 
(Numbers in parentheses refer to catalogue numbers of the specimens figured.) 
Figs. 1, 5, 9. Dorsal, front, and ventral views of broad, flat form of RhynchoneUa 
vellicata Hall. (M 45.) 
Figs. 2, 6, 10. Dorsal, front, and ventral view of median form of RhynchoneUa 
vellicata Hall. (M 45.) 
Figs. 3, 7, 11. Dorsal, front, and ventral view of narrow form of R. vellicata Hall. 
(M45a.) 
Figs. 4, 8, 12. Dorsal, front, and ventral view of a form intermediate between 
Hall's R. vellicata and R. mainensis Billings, labeled R. mainensis Bill. var. (M 21). 
Figs. 13, 16, 19. Dorsal, front, and ventral view of a very perfect specimen of R. 
mainensis Bill., near the form of Billings's type. (M 22.) 
Figs. 14, 17, 20, and 15, 18, 21. Dorsal, front, and ventral views of the broader, 
flatter forms of R. mainensis Billings. (M 19.) 
Figs. 22, 23, 24. Dorsal, front, and ventral views of R. mainens'is Billings, approach- 
ing the form R. abrupta Hall. (M 19.) 
1 The original figures from which Pis. I and II were prepared were made directly from the speci- 
mens by a patented photographic process by N. W. Carkhuff. 
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