Hydromys lutrilla Krefft

Parnaby, Harry E., Ingleby, Sandy & Divljan, Anja, 2017, Type Specimens of Non-fossil Mammals in the Australian Museum, Sydney, Records of the Australian Museum 69 (5), pp. 277-420 : 355-357

Hydromys lutrilla Krefft , in Gould, 1863a

The Mammals of Australia Part 13, page xxxvii. (1 May 1863) .

Common name. Water Rat.

Current name. Hydromys chrysogaster É. Geoffroy, 1804 ; following Jackson & Groves, 2015). Taxonomic status unresolved: a detailed taxonomic review of the extensive variation within Hydromys chrysogaster is needed, and two species could be present in south-eastern Australia (Jackson & Groves, 2015).

Holotype. PA.125, by subsequent determination. Indeterminate sex, skin mount, part skull in situ. Registered in Palmer Register in c. 1878 but no entry for locality, collector, donor or collection date. An entry in the notes column of the register, possibly written by Palmer, states: “drawing of this specimen by Angas, is referred to by Gould, is preserved in Australian Museum”. Donated by W. S. Macleay.

Condition. Skin mount (part skull in situ), missing upper incisors, snout area is damaged (parts of skin missing), tear in the right front limb, fracture in the proximal end of the tail. The sex could not be determined from the skin.

Type locality. Foreshore outside Elizabeth Bay House, Elizabeth Bay, Sydney ( Gould, 1863a), NSW, Australia.

Comments. Gould (1863a) states that lutrilla was known from a single specimen and Krefft (1864a) states that is was known from a single half grown specimen. Gould (1863a) remarked that, not having examined the specimen, he was unable to determine if it was a valid species. Although Gould attributed discovery of this entity to Macleay, Gould reproduced a description provided by Krefft and authorship is therefore attributed to Krefft (Article 50.1, the Code). The specimen currently believed to be the holotype is fully furred. Although this is inconsistent with the remark by Krefft (1871a) that “the original specimen in the Australian Museum has lost much of the fur …”, it is possible that the skin mount has been repaired. Krefft in Gould (1863a) gave four body measurements of the holotype which are a good fit with PA.125, given the relatively imprecise nature of the characters and possible skin shrinkage. These are (our measurements in brackets): “length from tip to tip”, 17 inches (16¾ inches); length of tail about 7 inches (7 inches); “length of face to base of ear”, 2 inches (2 inches); length of tarsi and toes, 2 inches (pes length without claws, 48 mm = 1.89 inches).

Mahoney & Richardson (1988) list 13 names under chrysogaster but do not discuss subspecific status. Troughton (e.g., 1941; 1974) recognized eight species of Hydromys in Australia, including H. chrysogaster lutrilla , one of several subspecies he recognized of H. chrysogaster . In the absence of any comprehensive taxonomic studies during the past 50 years, modern authors have defaulted to treating “ chrysogaster ” as a single variable species without recognizing subspecies, most of which are treated as invalid.