124 MOLLUSCA 



Order 2. Octopoda. 



Eight arms, suckers sessile. (Octopus, Argo- 

 nauta.) 

 Subclass 2. Tetrabranchiata. 



Tentacles numerous. External chambered 

 shell. Funnel open along one side. Only one 

 living genus. Four gills. (Nautilus.) 

 Brooks: The Origin of the Oldest Fossils and the Discovery of the 



Bottom of the Ocean. Smithsonian Rept., 1894. 

 Coe: Sexual Rhythm in Teredo. Science, 80, 1934. 

 Kellogg: Contribution to our Knowledge of the Morphology of Lamelli- 

 branchiate Mollusks. Bull. U. S. Fish Com., 1890. 



: Shell-fish Industries. Henry Holt and Co., 1910. 



: Ciliary Mechanisms of Lamellibranches, with Description of 



Anatomy. Jour. Morph., 26, 1915. 

 Pelseneer: Contribution a L 'Etude des Lamellibranches. Arch. d. Biol., 

 11, 1891. 



: Recherches Morphologiques et Phylogenetiques sur les Mol- 



lusques Archaiques. Acad. roy. d. Sci. d. lettres et d. beaux-arts d. 



Belgique, 1899. 



Etude sur des Gastropodes Pulmones. Mem. Acad. roy. d. Sci. d. 



lettres et d. beaux-arts de Belgique, 1901. 

 Ridewood: On the Structure of the Gills of Lamellibranchs. Phil. 



Trans. Roy. Soc, London, B, 195, 1903. 

 Stenta: Zur Kenntnis der Stromungen im Mantelraume der Lamelli- 



branchiaten. Arb. Zool. Inst. Univ. Wien, 14, 1902. 



PELECYPODA 



VENUS MERCENARIA (Quahog) 1 



Animals of this species wander around over muddy bot- 

 toms in rather shallow water, keeping the siphon end, at 

 least, above the surface of the mud. If possible, you should 

 find specimens in their native places and watch their move- 

 ments. Specimens placed in water and left undisturbed for 

 some hours are likely to protrude the siphons, and the foot 

 may be protruded in some cases. 2 Allow powdered carmine 

 to settle slowly past the openings of the siphons and deter- 

 mine the direction of the current of water for each. Touch 



1 Points in which the fresh-water mussel differ have been noted, so 

 the directions may be used for that form. 



2 Other species of lamellibranchs are more satisfactory than Venus 

 for studying movements, as they expand quickly after being disturbed. 

 Among the common ones that may be mentioned are Ensis, Cumingia, 

 Yoldia, and Mytilus. 



