XXll 
INTEODUCTION. 
To Dr. Henry Woodward I am again indebted for many valuable 
suggestions while supervising the work throughout its progress. 
Mr. G. C. Crick has again done me the impoitant service of 
looking over the proofs, and of giving me the benefit of his criti- 
cisms on many points, and Mr. B. B. Woodward has helped me in 
connection with the literature of the fossil Cephalopoda. 
London, 
February 12th, 1891. 
ABTHUR H. FOORD. 
