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rOPULAR SCIENCE REVIEW. 
Fig. 2. Sepia. Dorsal aspect. 
s sepiostaire, tlie mantle being cut and reflected. 
„ 3. Female Argonaut. 
p expanded arm applied to tbe outside of the pedal shell. 
„ 4. Male Argonaut. 
h the arm which becomes detached (hectocotylus). 
„ 5. Pen. 
„ 6. Nautilus, with its external siphunculate chambered pallial shell 
partly cut, to show s the siphuncle traversing the septa sepa- 
rating c <? c, some of the chambers. 
„ 7. An Ammonite vertically bisected, to show the whole series of 
chambers. 
