Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
līnĕālis, e, adj. [linea], consisting of lines, made with lines, lineal (post-class.): ambitus lineales, Amm. 22, 16, 7.
Hence, adv.: līnĕālĭter, in the manner of lines, by means of lines: quos (circulos) linealiter feci, Mart. Cap. 8, § 834.