DR. F. A. JENTINK. MAMMALS. 169 



N°. 41g. Young adult cf. Round Bivak Island, January 17. 1910 (skin and skeleton). 

 N°. 426. Young adult cf. Round Bivak Island, January 24. 1910 (skin and skeleton). 

 N°. 498. Very old Q. Round Bivak Island, Mardi 8. 1910 (skin and skeleton). 

 N°. 500. Old Ç. Round Bivak Island, March 10. 1910 (skin and sketelon). 



This species has a large geographical distribution ; the type-specimen has been collected 

 near Port Moresby, the spécimen mentioned in my paper in „Nova Guinea", Vol. IX, p. 5, 

 originated from Sabang,. wher'eas there is in our collection a spécimen from the Huon Gulf. Thèse 

 three spécimens are maies; but at présent possessing two (N° s . 498 and 500) females, we 

 could convince ourself that there are no sexual différences. 



Mr. OLDFIELD Thomas remarked in his original description of esox (Ann. and Mag. 

 Nat. Hist. 1906, p. 325) that the type-specimen had two fifths of its tail white, being one 

 of the différences between it and Hydromys Beccarii Peters, the latter having that organ for 

 two thirds white; our large séries however shows that this character cannot hold as no 

 two individuals présent the same proportion in distribution of white and black on the tail ; 

 in N°. 90 the proportion is 2 / 3 ; in N°. 394, 4 / 3 ; in N°. 396, */, ; in N°. 419, l / s ; in N°. 426, 3 / 2 ; 

 in N°. 49S, I '. 1 ; and in N°. 500, Y 3 > nieanwhile it was in our Sabang-specimen 2 / 5 , and in a 

 spécimen in our collection from the Huon Gulf '/ 3 \ 



The number of thoracic and lumbar vertebrae taken together is larger in Hydromys 

 than in any other hitherto studied skeleton of an East Indian rodent. Hydromys has 14 thoracic and 

 7 lumbar vertebrae, Pogonomys 13 thoracic and 7 lumbar vertebrae, Mus 13 thoracic and 6 

 lumbar vertebrae ; thèse numbers I took from our fresh skeletons, larger in number than 

 hitherto examined, as generally skeletons of rodents are rarities in zoological collections. The 

 number of segments of mesosternum — four — is the same in two of the three above mentioned 

 gênera, viz. Pogonomys and Mus, in Hydromys however there are five mesosternal-segments, 

 ail well developed. The presternum of Hydromys is less crested than in the other two gênera. 

 Very striking is the very pronounced flattened shape of the tail-vertebrae of Hydromys; 

 from the tenth vertebra- downward they are so broad that in their middle they are about as 

 broad as at their extremities. 



Measurements taken in the flesh, in millimeters : 



. 

 90 394 39 6 — H9 — 4^ — 49_8 — 5_oo 



head and body 300 — 276 — 309 — 275 — 250 — 270 — 300 



tail 245 — 249 — 257 — 210 — 230 — 200 — 230 



hind foot 61 — 56 — 59 — 56 — 54 — 54 — 54 



ear 16 — 18 — 18 — 16 — 16 — 16 — 16 



skull: basai length ... 49 — 48 — 49 — 44.5 — 45 — 47 — 47 



zygomatic breadth . 27.5 — 26.5 — 26 — 23.5 — 24 — 25 — 27 



diastema 16.5— 15 — i'S — 13-5 — ij-5 — 13-5 — IS 



upper molar séries . 8.5 — 8 — 8.5 — 8.5 — 8 — 8 — 8 



We see how large the différences are in thèse measurements, and that they hâve 

 nothing to do with âge or sex, like there was an endless différence in the distribution of 

 white on the tail independent of âge and sex ; and I may add that as to the colour of the 

 animais the same great variation is to be seen, especially in the colour of the lower parts ; 



