394 MR. OLDFIELD THOMAS ON MAMMALS 



another to the links that connect the aberrant Bydromys with the true Murinre, and is 

 indeed the last link needed. For we may take five main characters as distinguishing 

 Hydromys from an ordinary Mus, viz.: (1) aquatic form; (2) flattened skull; (-3) 

 reduced plate to zygoma-root; (4) two molars only; and (5) peculiar molar structure. 

 The first discovered linking genus, Xeromys, was murine as to 1, 2, and 3, hydromyine 

 as to 4 and 5 ; then came Chrotomys, murine as to 1, 2, and 4, hydromyine as to 3 and 5. 

 Celcenomys, described above, is like Chrotomys, but also hydromyine as to 4 ; and now 

 comes Crummys, murine as to 1, 4, and to a certain extent the highly important 5 

 (molar structure), but with the hydromyine 2 and 3, in addition to the short palatal 

 foramina found in all the genera mentioned. 



Like all annectant genera, Crunomys is most difficult to place satisfactorily in the 

 system, and it is only with much hesitation that I have included it in the Hydromyiiise, 

 a position which will have to be revised when specimens showing the unworn dentition, 

 the mammary formula, and other characters are available for examination. 



The following is a rough synopsis of the genera now considered to belong to the 

 Hydromyinae^ : — 



Molars f . 



Aquatic. Skull flattened ; frontal profile concave 1. Hydromys. 



Terrestrial. Skull rounded ; frontal profile normal 



Outer wall of anteorbital foramen slightly projectcfl forward ... 3. Xeromys. 



Outer wall of anteorbital foramen not projected forward .... 3. Celanomys. 



Molars |. 



Molars strietlv hvdromyiue in structure. Back striped. Fur soft, "i 



•' . •' V i. Chrotomys. 



Terrestrial, fossorial J 



Molars more murine. Back unstriped. Fur spiny. Semi-aquatic . . 5. Crunomys. 

 The first two are Australian, the last three Philippine. 



• Ckusomys f.\llax, sp. n.2 (Plate XXXIII. fig. 1.) 

 Size about as in Xeromys vvyoides. Fur short and close, profusely mixed with 

 flattened spines ; neither hairs nor spines longer than about 6 mm. on the back. 

 General colour pale greyish, lined with yellowish on the back. Dorsal spines white, 

 darkening to black at their tips. Belly dirty greyish white, not sharply defined, the 

 hairs slaty basally, dull whitish terminally. Sides of muzzle brown. Whiskers 

 numerous, long, mixed black and white. Ears short, uniformly brown. Hands and 

 feet greyish brown on the metapodials, lightening to white on the digits ; fifth hind toe 



' Since this paper was read an additional genus, Lepiomijs, has been described from New Guiuea (Ann. 

 Mus. Genov. (2) xviii. 1897). It has |- molars, like Chrotomys and Crunomys. 



* See preliminary diagnosis in Minutes of P. Z. S. for June 15, 1897 (published June 19). 



