Manchester Memoirs, Voi. x/vnz. (igo4), No. *^t. i 



XXI. A Diagnostic Key to the Genera of Recent 

 Dibranchiate Cephalopoda. 



By William E. Hoyle, D.Sc . 



Received and Read February 2nd, 1^04^ 



The subjoined key has been drawn up in preparation 

 for a systematic account of the recent Cephalopoda to be 

 published in the " Tierreich," undertaken by the German 

 Zoological Society and continued by the Berlin Academy 

 of Sciences. Publicity is now given to it, in the hope that 

 my colleagues, who attempt to identify specimens by its 

 means, will communicate with me regarding any difficulties 

 or equivocal results which they may encounter. 



In its elaboration the attempt has been made to utilise 

 external characters alone, and to resort to internal struc- 

 ture only when necessary. This is the main cause of the 

 differences between the scheme here presented and those 

 of Mr. Goodrich* and Dr. Pfefifer,-f- who have published 

 keys for the discrimination of the CEgopsida. The memoir 

 of the latter author, the result of years of work at this 

 group and of an unrivalled acquaintance with immature 

 forms, has been of the greatest assistance to me, and if I 

 have not followed him in all his conclusions I have 

 ventured to reject them only with diffidence. If I may 

 say so, I think he is a little too disposed to lump species 

 and to split genera. The result is seen in the fact that of 

 his 50 genera 43 contain only one species each. 



* "Note on a Large 'iqmA" Joiirii. Mar. Biol. Assoc, ■ n.s., vol; 2'. 

 p. 318—321, 1892. 



t " Synopsis der oegopsidea Cephalopoden," Mitt. Naturhist^ Mus. 

 \2 Beiheft Jahrb. Hamburg. Wiss. Anst., vol. 17), vol. 17, p. 147 — 198, 

 1900. In addition to being indebted to Dr. Pfeffer's published writings I 

 have to thank him for information given both in conversation and by letter. 



J7(ne 17th, igo4. 



