A 42 year old woman has had a feeling of abdominal discomfo for the past 8 months. Abdominal CT scan demonstrates a 6 cm cystic mass involving the right ovary with small areas of calcification. Post removal, the ovary grossly, the mass on sectioning is filled with abundant hair and sebum. Microscopically, the mass has glandular spaces lined by columnar epithelium, squamous epithelium with hair follicles, cailage, and dense connective tissue. What type of tumour is it?