Ans. c (Platypelloid) (Ref. Dutta Obstetrics 6th ed., p 90)SACROCOTYLOID DIAMETER (9.5 cm)# It is the distance between the mid point of the sacral promontory to iliopubic eminence.# It represents the space occupied by the biparietal dimeter of the head while negotiating the brim of flat pelvis.# Flat pelvis (transversely ovalI Platypelloid pelvis) is characterized by shortest sacrocotyloid diameter causing narrowing of pelvis from side to side.