With adult shells reaching only about 2 mm (about 0.08 inch) in diameter, Teinostoma biscaynense Pilsbry & McGinty, 1945 is one of the smallest members of the family Tornidae in the western Atlantic. The shell has a low spire, is flattened, depressed, and its periphery (outer shell “edge”) is softly angled. The shell spire and base lack any sculpture except for coarse, irregular growth lines. The protoconch is sunken within the adult shell. The umbilicus is completely obliterated by a whitish, opaque callus that contrasts in color with the translucent-white remainder of the shell. (The species was named after Biscayne Bay in South Florida.)