FOSSIL CEPHALOPODS. 



323 



are also met with, chiefly in the Oxford and Kim- 

 meridge Clays, where they have been so well preserved 

 that even their " ink-bags " are fossilized — clays being 

 always the best preserving grounds for fossils. After 

 the long periods of time which have elapsed since the 

 ancient creatures secreted the pigment, it is still avail- 



Fig- 331- — Bactilites vertebralls : c, cast of detached chamber. 



able, and I have seen sketches in sepia made en- 

 tirely from the fossil ink of extinct cuttle-fishes ! 



The limits of space prevent me doing more than 

 merely sketching the outlines of the history and 

 affinities of our most interesting and common fossils. 

 The student who collects will soon learn more about 

 them ; particularly in the magnificent volumes pub- 



