Microhydromys richardsoni Tate and Archbold 1941

Microhydromys richardsoni Tate and Archbold 1941, Am. Mus . Novit., 1101: 2.

Type Locality: New Guinea, Prov. of Papua (= Irian Jaya), Snow Mtns (Pegunungan Maoke), Idenburg River, 4 km SW Bernhard Camp, 850 m.

Vernacular Names: Richardson's Shrew Mouse.

Distribution: New Guinea; scattered localities in hill forest from type locality in Prov. of Papua east to Sogeri in Port Moresby region (Flannery, 1995 a:248).

Conservation: IUCN – Lower Risk (nt).

Discussion: The smallest-bodied of New Guinea’s endemic murids, the only one among members of the Hydromys and Xeromys Divisions with longitudinally grooved upper incisors, and known only by five specimens (Flannery, 1995 a). Distributional and biological data summarized by Flannery (1989, 1990 b, 1995 a). In its morphological structure, M. richardsoni is a miniature version of Hydromys but with grooved upper incisors and strictly terrestrial rather than amphibious habitus. It also possesses the primitive cephalic arterial pattern, a conformation shared with species of Xeromys, Crossomys, Hydromys, Paraleptomys, and Parahydromys, but not with Leptomys or the terrestrial New Guinea shrew mice in Pseudohydromys (which includes Mayermys and Neohydromys) that exhibit a derived configuration. Whether the same pattern is present in M. musseri has yet to be determined.