182 DE. B. A. BENSLEi' OX THE EVOLUTION 



Winge (1893), wlio lias made a carefvil study of tlie existing Didelpliyidae, divides the 

 family as follows * : — 



I. Hindmost of tlie three outer cusps of the upper molars well developed. 



A. p. 1 and m. 3 comparatively well developed. Molar teeth with high sharp cusps. Body of the 



lower jaw sliallow. Proc. angularis sharply inflected. Ribs narrow. No marsupium. 

 GrymcBomys \_ = Marmosa\. 



B. p. 1 and m. 3 reduced. Molar teeth with low rounded cusps. Body of the lower jaw deep. 



Proc. angularis only slightly inflected. Ribs broad. Marsupium in the form of folds. 

 Philander [=Caluromys]. 



II. Hindmost of the three outer cusps of the upper molars reduced. 



A. Tail long. Terminal phalanx of hallux broad. 



(a) ISo swimming-membrane between the toes. Skin of palms and soles normal. 



DideJphys [ = Didelphys and Metachirus] . 



[b) Swimming-membrane between toes. Skin of palms and soles provided with peculiar 



papillae. 



Chironectes. 



B. Tail short. Terminal phalanx of hallux compressed. 



Hemiurus [^^^Peramys]. 



He considers the relationships of the above genei'a to be as follows : — ■ 



Chironectes. Peramys. 



Philander. Dideljpiys. 



\ I 



Urymceomys. 



The genus Feramys is regarded by Winge as derivative of Didelphys, but iu many 

 respects it is prototypal not only to that genus but also to Marmoset. It will be observed 

 that Winge's main division associating Dldelphi/s and Ferami/s is based on the characters 

 of those elements of the upper molars here referred to as external styles. These structures 

 are regarded by him as typically three in number and as the original cusps of the crown 

 (triconodont type). Winge remarks with reference to Fhascogale, Dasijurus, and their 

 allies in the Dasyuridae that they present a more primitive condition of the upper molars 

 than is found in any other of the existing Mammalia, the three outer cusps being 

 persistent, and the median one of them, like the median one of the three internal cusps 

 of the lower molars, being larger than the others. He also states that in Gnjmceomys 

 (3farmosa) the three outer cusi^s are present, but the median one has lost its j)re- 

 dominance, while again in Hemiurus {Feramys) and in Didelphys the hindmost cusp 

 has become reduced. He illustrates these cases by the teeth o'i PJiascogale penicillata, 

 JIarmosa cinerea, and Feramys domestica, designating the three cusps numerically in 

 the order of their occurrence from before backwards. 



* On account of these results being written in the Danish language the writer lias taken the liberty to substitute 

 a translation for the original text. 



