OCTOPODA. 88 1 



more or less feather-shaped, and consists of a central shaft bordered 

 by lateral wings. In some cases, as in Leptoteuthis and Pksioteuthis, 

 the actual impression of the body of the animal is preserved, and 

 from such examples it is known that the arms were not furnished 

 with horny hooks. 



Sub-Order II. Octopoda. 



The forms included in this section of the Dibranchiates are char- 

 acterised by the possession of eight equal arms, the internal skeleton 

 being rudimentary or absent. The suckers of the arms may be 

 modified into horny hooklets. In the female of the Paper Nautilus 

 {Argonauta) the two dorsal arms are widely expanded, and secrete 

 a delicate calcareous external shell, which is not connected by 

 muscles with the body of the animal. The shell of the female Ar- 

 gonaut is one-chambered, spirally coiled and involute, its external 

 border being keeled, and its surface tuberculated. The genus is 

 represented in the Pliocene Tertiary by one or two species, and 

 several living forms are known. 



According to von Zittel, the genus Acanthoteuthis is founded upon 

 the remains of an Octopod Cuttle-fish preserved in the fine-grained 

 Lithographic Limestone (Jurassic) of Solenhofen, and showing the 

 form of the body and the outline of the arms, the latter carrying 

 each two rows of falciform horny hooks. 



LITERATURE OF MOLLUSCA. 



General. 



i. " Manuel de Conchyliologie et de Paleontologie Conchyliologique." 

 Paul Fischer. 1887. 



2. " Handbuch der Palaeontologie." Bd. I. Abth. 2, Lief. 1-3. 1881-84. 



Von Zittel. 



3. " Manual of the Mollusca." S. P. Woodward. 4th ed., with " Ap- 



pendix of Recent and Fossil Conchological Discoveries," by 

 Ralph Tate. 1880. 



4. " Handbuch der Conchyliologie." Philippi. 1853. 



5. " Malacozoa." In ' Bronn's Klassen und Ordnungen des Thier- 



Reichs.' 1862-66. Keferstein. 



6. " Traite elementaire de Conchyliologie." 1835-39. Deshayes. 



7. " The Genera of Recent Mollusca." 1858. H. and A. Adams. 



8. " Mineral Conchology of Great Britain." 1812-30. J. Sowerby. 



Lamellibran'chiata. 



[Apart from the general works above quoted, the following are some of 

 the more important sources of original information, with more 

 especial reference to the fossil forms.] 



9. " On the Microscopic Structure of Shells." ' Reports of the British 



Association.' 1844 and 1847. W. B. Carpenter. 

 VOL. 1. 3 K 



