Conjunctival squamous cell carcinoma (SCC) and conjunctival melanoma are both malignant tumors of the conjunctiva but differ in their cell origins and behavior. SCC originates from the squamous epithelial cells of the conjunctiva, while conjunctival melanoma arises from melanocytes, the pigment-producing cells. Melanomas often present as darkly pigmented lesions and are generally more aggressive than SCC.