PLATE VII. 



Cyrtoceras falx (page 32). 



Figure 1. Cyrtoceras falx, Billings. Side view and section of the larger end, 

 the siphon on the outer (ventral) side of the curve. 



" 2. Section (with siphuncle) of a more compressed form, the compres- 

 sion partly due to pressure. The tube becomes more and more 

 cylindrical in age. 



" 3, 3a. A younger specimen, from the Ottawa limestone. 



" 4. A worn specimen, shewing the close septa. 



Cyrtoceras Billingsii (page 33). 



5. Cyrtoceras Billingsii (C lamellosum., Hall). Side view. 5* is the 



section at the larger end ; 5** of the smaller cylindrical end — 

 the siphon external. 



6. A younger specimen, with closer lamellaa of growth. 



