The stem is attached at the concave margin, where the cap is auriculate and has a prominent boss or elevation, and bent at right angles with a characteristic curve.    From Wordnik.com.  [Studies of American Fungi. Mushrooms, Edible, Poisonous, etc.] Reference

Bases acuminate: coming to a sharp, narrow, prolonged point. acute: coming to a sharp, but not prolonged point. auriculate: ear-shaped cordate: heart-shaped with the norch away from the stem. cuneate: wedge-shaped. hastate: shaped like an halberd and with the basal lobes pointing outward. oblique: slanting. reniform: kidney-shaped but rounder and broader than long. rounded: curving shape. sagittate: shaped like an arrowhead and with the acute basal lobes pointing downward. truncate: ending abruptly with a flat end, that looks cut off.    From Wordnik.com.  [Wikibooks - Recent changes [en]] Reference