Which type of tumor is described as a benign epithelial tumor forming a rounded mass?

The description of a benign epithelial tumor forming a rounded mass aligns perfectly with a papilloma. Papillomas are characterized by their projection from the surface of the skin or mucous membrane, resulting in a rounded mass that often resembles a wart. They are formed by an overgrowth of epithelial cells and can vary in size and shape.

The other options, while related to skin conditions, do not fit the specific characteristics of a rounded mass benign epithelial tumor. Dermatosis Papulosa Nigra refers to small, benign hyperpigmented lesions commonly found in individuals with darker skin, typically not described as rounded masses. Naevae, commonly known as moles, are also benign but are not strictly epithelial tumors formed into a rounded mass. Lentigo refers to pigmented lesions caused by an increase in melanin and often presents as flat spots rather than raised tumors. Thus, the clear identification of a papilloma accurately captures the essence of the question regarding benign epithelial tumors.