It's still lutreola not lutreolus?

AMTC lists it as Rattus lutreola: "lutreola was the original spelling of the species epithet by J.E. Gray, 1841; subsequently also used by Thomas, 1921 and Finalyson, 1935. Recently represented as lutreola in international mammal species lists. REFERENCES: Gray, J.E. 1841. Contributions towards the geographical distribution of the Mammalia in Australia, with notes on some recently discovered species, in a letter addressed to the Author. Appendix C. pp. 397-414 in Grey, G. (ed.). Journals of Two Expeditions of Discovery in North-west and Western Australia During the Years 1837, 38, and 39, Under the Authority of Her Majesty's Government. Describing many newly discovered, important, and fertile districts, with observations on the moral and physical condition of the aboriginal inhabitants, &c. &c. London : T. & W. Boone Vol. 2 vii 482 pp. [Date published Nov. 1841] [page 409]"
If lutreol- is an adjective, then it should be -us (as the accompanying noun Rattus is masculine, 2nd declension). However, if it is a noun ('little otter'), then it should be -a (as Lutra is feminin, 1st declension).