This is a simplified form of the Curved Triangle that appears on page 92 of Stewart's book (Example 4, 2nd edition only) [I finally got a copy!]. The form presented here differs from Stewart's in that it simply uses prisms and doesn't fret that many faces are coplanar. This Curved Triangle is composed from 3-pentagonal/2-triangular prism arcs from the 30-gon Circle of Prisms (also from Stewart's book). I used Geomag Pastelles for this construction.