Another classification of Incidence Scrolls
  The aim of this paper is the computation of the degree and genus of all incidence scrolls in Pn. For this, we fix the dimension of a linear space which have a base space of this fixed dimension. In this way, we can obtain all the incidence scrolls with a line as directrix curve, those whose base contains a plane, and so on. 
Rosa Cid and Manuel Pedreira