304 MARINE INVERTEBRATES 
Porcelanous : Resembling porcelain. 
Rad'ula: Same as lingual ribbon. 
Reticulated: Having distinct lines or veins crossing like a net- 
work ; covered with netted lines. 
Sculpture: Elevated or impressed marks on the surface; mark- 
ings resulting from irregularity of surface; tracery. 
Sinistral : Having the aperture of the shell at the left ; opposite 
of dextral. 
Sinuate: Curved in and out; wavy. 
Siphon: A tubular fold, or prolongation of the mantle forming 
a tube. 
Spire: All the whorls of a spiral univalve, above the first 
large body-whorl. 
Suture: The line of junction of the successive whorls of a uni- 
valve shell, or the line of closure of the opposite valves of a 
bivalve shell. 
Teeth : Tooth-like projections on the hinge of a bivalve shell. 
Testaceous : Having a hard shell, as distinguished from crusta- 
ceous, or soft-shelled. 
Turbinate: Shaped like a whipping-top ; whorled from a broad 
base to an apex. 
Umbilicus: A central, navel-like depression in the body-whorl; 
a circular, more or less central pit or hollow. 
Umbo: The beak of a bivalve shell; the protuberance of each 
valve above the hinge. 
Varices, plural of Varia: Raised marks on the shell denoting 
a former position of the lip of the aperture, and indicating periods 
of rest. 
Varicose: Having prominent and tortuous formations on the 
shell. 
Ventricose: Having the whorls of the shell swollen or strongly 
convex. 
Whorl: One of the turns of a spiral shell. Body-whorl, the 
last whorl. 
