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. 
Lamelliform: Lamellate in structure; disposed in leaf-like 
layers. 
Lingual ribbon: The chitinous band of teeth, or rasp, borne 
upon the odontophore; the radula. 
Iunule: 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. 
Pallial line: The impression or mark made by the mantle, or 
pallium, on the inner surface of a bivalve shell. 
Pallial sinus: A notch or recess of the pallial line; the scar of 
the siphon. 
Papillaceous: Warty; studded with bosses; having excres- 
cences. 
Perios’tracum : Same as epidermis. 
Per’istome : In zodlogy, mouth-parts in general ; in conchology, 
the margin of the aperture of the shell. 
