598 MR. R. I. POCOCK ON THE 



inferior notch turns inwards above towards the posterior end of 

 the supratragus, and it is provided with a shallow pouch defined 

 externally by a definite thickened ridge. 



The ear of Phalanger maculatus is greatly reduced, thickly 

 covered with hair externally, and scarcely projects above the level 

 of the head. The supratragus is large and valvular, and the 

 cavity of the ear above it is deep and roofed over by a ridge 

 resulting possibly from the confluence of lobate thickenings 

 homologous to the two seen in Phalanger. The anterior lidge 

 does not extend so high above the supratragus as in the two 

 genera already discussed, and there is a trace of the pouch on 

 the posterior ridge, although it is not so well defined as in 

 Pseudochirus. 



In Phascolarctos the ear is more expanded even than in 

 Pseudochirus., but it dijBfers from the ear of that genus, Tricho- 

 surus, and Phalanger in having the supratragus reduced to a low 

 curved ridge without any trace of the lobe *. There is a low 

 ridge above it as in Trichositrus, and the anterior ridge bounding 

 the cavity of the ear in front is as in that genus ; the tragus, 

 however, is much smaller. The pocket on the posterior ridge is 

 present as in Pseudochims, but is deeper and has a more sharply 

 defined posterior rim. 



In Phascolomys the antero-internal I'idge, continuous above 

 with the slightly overfolded anterior margin of the pinna, is 

 produced inferiorly into a large compressed lamina, jutting back- 

 wards into the cavity of the ear and descending to the auditory 

 orifice. Anteriorly and externally this lamina is marked by a 

 deep groove which descends and passes into a low ridge defining 

 the anterior border of the inferior notch, but there is no definite 

 tragal thickening. The antitragal ridge is also simple. It 

 ascends and forms the posterior edge of the cavity of the pinna, 

 and is itself marked externally and posteriorly by a groove. 

 The supratragus appears to be represented by a low ridge visible 

 above the laminate expansion of the antero-internal ridge. 



Tlie ear of Lasiorhinus latifrons is very like that of Phascolomys, 

 but is longer. On a skin softened in water I could find no trace 

 of the supratragus. 



The ear of Phascolomys resembles that of Phascolarctos in the 

 complete or almost complete disappearance of the supratragus — 

 an important character considering the constancy in the deve- 

 lopment of this ridge in many Mammals, But in the simple 

 structure of the posterior antitragal ridge it is more like that of 

 Trichosurus. 



The differential chai^acters of the ear may be used to define and 

 classify the five genera as follows : — 



a. Supratragus represented by a strong ridge with well-developed 

 lobate thickening. 



h. No pocket above the antitragal ridge Trichosurus. 



* Thomas mentioned this peculiarity and wrote "metatragus almost obsolete." 



