Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Jūra, ae (also Jūres, ĭum, m., Plin. 3, 4, 5, § 31; 16, 39, 76, § 197), m., a chain of mountains extending from the Rhine to the Rhone, Caes. B. G. 1, 2.
Hence, Jūren-sis, e, adj., of Mount Jura, Sid. Ep. 4, 25.