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NAUTILID^. 
I. Partitions of the chamhers with simple margins, forming harmonic 
sutures. 
a. Shell spiral 
h. Whorls discoid. 
c. Last chambers produced. 
Spirula. 
Spirolina. 
cc. Last chambers uniform. 
d. Sides similar, the mouth mesial. 
Nautilus. 
dd. Sides dissimilar, convex above> flat beneath, the 
mouth lateral. 
Rotalia. 
Lobatula. 
Nummulita. 
bh. Whorls globular. 
Vermiculum. 
Arethusa. 
Lagenula. 
aa. Shell produced. 
Orthocera. 
Belemnita. 
Conularia. 
II. Partitions of the chamhers with waved margins forming serrated 
sutures. 
a. Spiral. 
h. Spirally discoid. 
Ammmita. 
Orbulita. 
Scaphita. 
hh. Spirally turrited, 
Turrilita. 
aa. Shell straight or bent. 
BacuUta. 
Amplexus. 
