1) Depressed 2) Flattened 3) Having a surbase 
• (a.) Having the vertical height from springing line to crown less than the half span; -- said of an arch; as, a segmental arch is surbased. • (a.) Having a surbase, or molding above the base.
Sur'based` adjective (Architecture) (a) Having a surbase, or molding above the base. (b) [ French surbaissé .] Having the vertical height from springing line to crown less than the half span; -- said of an arch; as, a segmental arch is surbased . 
having a surbase. · depressed; flattened. · (of an arch) having a rise of less than half the span.