DEFINITION OF TERMS 303 



Decussated: Crossed; intersected. 



Dextral : Having the aperture on the right side of the shell 

 when the apex is upward. 



Epidermis : The horny coating or outer skin of some shells. 



Foot: The ventral surface of the body on which the animal 

 rests or moves. 



Fossette : A little hollow or pit. 



Fuscous: Brown tinged with gray; swarthy. 



Fusiform : Tapering both ways from the middle. 



Lamettiform: Lamellate in structure; disposed in leaf -like 

 layers. 



Lingual ribbon : The chitinous band of teeth, or rasp, borne 

 upon the odontophore ; the radula. 



iM-nule : An impressed area just below the beaks of bivalve shells. 



Mantle: A fleshy or membranous outgrowth of the outer body- 

 wall ; also called pallium. 



Mantle cavity : The space between the mantle and the body. 



Monomyarian : Having one adductor muscle, as an oyster. 



Nephridium : The renal organ of mollusks, corresponding to 

 kidneys in vertebrates. 



Node : A knob or protuberance ; also a notch in the margin. 



Odon'tophore : The lingual ribbon bearing chitinous teeth. 



Oper'culum: A horny or shelly plate which serves to close the 

 aperture of the shell when the animal is retracted. 



Osphra'dia, plural of Osphradium : Olfactory or water-testing 

 organs. 



Otocyst : The cavity, or cyst, which contains the essential parts 

 of an organ of hearing. 



PaUial line: The impression or mark made by the mantle, or 

 pallium, on the inner surface of a bivalve shell. 



PaUial sinus : A notch or recess of the pallial line ; the scar of 

 the siphon. 



Papittaceous : Warty ; studded with bosses ; having excres- 

 cences. 



Perios'tracum : Same as epidermis. 



Per'istome : In zoology, mouth-parts in general ; in conchology; 

 the margin of the aperture of the shell. 



