The Collaborative International Dictionary of English v.0.48:

Wentletrap \Wen"tle*trap`\, n. [D. wenteltrap a winding
   staircase; cf. G. wendeltreppe.] [Obs.]
   Any one of numerous species of elegant, usually white, marine
   shells of the genus Scalaria, especially Scalaria pretiosa,
   which was formerly highly valued; -- called also staircase
   shell. See Scalaria.
   [1913 Webster]