Nuculana platessa: Shell thin, flat, smooth, whitish, nearly straight; sculpture only of faint incremental lines; epidermis pale straw-color, translucent, polished; beaks small, bulbous, but inconspicuous, or hardly elevated above the hinge-line; lunule so narrow as to be obsolete; escutcheon extremely narrow, long, bordered by a faint thread, below which is a still fainter one; base arcuate; anterior end evenly rounded, short; posterior end straight, squarely, not obliquely, rounded-truncate; interior polished, rostrum with a mesial septum most elevated distally, nearly central; fossette narrow, elongated, parallel with the cardinal margin; teeth very small, anterior series with four undeveloped and seven elevated teeth ; posterior series with about twenty-five developed and eight or nine (?) undeveloped arched teeth; interior of shell polished, not showing the scars. Maximum longitude of shell 10.3; altitude 4.4; diameter 2; vertical of the beaks from anterior end 3.25mm.

Nuculana platessa: The nearest relative of this shell is N. carpenteri Dall, from the eastern coast of the United States and the Antilles. The latter has the rostrum much more slender and more recurved, the lunule, and especially the escutcheon, wider and better defined, and the curve of the anterior end more pointed in the middle. The central part of the base below the beaks is also, in harmony with the general curvature of the shell, proportionally more produced, The number of teeth on the hinge-line is smaller, the fossette shorter and wider, and the rostral septem more dorsally situated.
This species recalls, to some extent, N. bushiana Verrill, but that species is more elevated and has sparse, prominent concentric lamella3 over part of its surface.

Nuculana platessa: Brazil. East from Rio Janeiro