108 



PALEONTOLOGY. 



The various forms of the extinct Belemnitidce constituted 

 one family in the Decapod tribe. The little Spirula, charac- 

 terised by a less complex, but internal chambered shell, is the 



Fig. 32. 

 Sepia officinalis (one-fourth natural size). 



type of a second family The cuttle-fish (Sepia, fig. 32), 

 known by its internal calcareous shell which remotely repre- 

 sents that of the Belemnite, exemplifies a third family of 



