Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† mītŭlus and mȳtŭlus (mȳtĭlus), n, m., = μύτυλος, a kind of mussel, seamussel, Plin. 9, 51, 74, § 160; 32, 9, 36, § 111; also, mutulus, Cato, R. R. 158; Hor. S. 2, 4, 28.