EXTERNAL CHARACTERS OF THE KOALA, 



599 



6'. A pocket above the autitragal ridge. 



c. Pinna greatly reduced ; pocket small Fhalanger. 



c'. Pinna large ; pocket better developed Pseudoch iriis. 



a'. Supratragus at most represented by a low curved ridge; 

 without trace of lobate thickening. 

 d. Antero-internal ridge normally developed; a large pocket 



above the autitragal ridge Phascolarctos. 



d'. Antero-internal ridge large and laminate ; no pocket above 



autitragal ridge Phascolomys. 



The Fore Foot. — In Trichosurus, Fhalanger, and Pseudochirus 

 there is a tuft of long carpal vibrissse. In Phascolarctos and 

 Phascolomys these tactile bristles are absent. 



In Trichosurus the fore foot presents no special modifications. 

 The five digits are free of webbing down to the plantar pads and 

 are nearly evenly spaced, the third and fourth being the longest 

 and subequal. the second and fifth a little shorter but subequal 

 and rising at approximately the same level, and the first or 

 pollex much the shortest, about two-thirds the length of the third 

 or fourth, and not opposable but closing obliquely backwards and 

 inwards across the sole (palm). The claws of all the digits are 

 compressed, curved, and pointed, and the integument of the 

 lower side of the digits is transversely grooved. The uniformly 

 granular plantar pad is four-lobed, the three main lobes being in 

 contact. The inner or pollical lobe, sometimes separated from 

 the main lobes, is fused with the inner element of the carpal pad 

 into a longitudinal mass, longer than wide. The external element 

 of the carpal pad is elliptical, narrowly separated in front from 

 the external lobe of the plantar pad, and, like the internal element, 

 passes imperceptibly proximally into a narrow naked area of skin 

 between them and the hair of the wrist. The centre of the sole 

 is depressed and granular like the pads and the depressions 

 between them. 



In Fhalanger the fore foot is considerably modified from the 

 type seen in Trichosurus. The third, fourth, and fifth digits are 

 evenly spaced ; but the second is capable of being separated from 

 the third by a much greater space than that between the third 

 and fourth. With tlie pollex it is capable of being extended 

 almost at right angles to the axis of the foot and of being closed 

 transversely upon the sole. The pads are transversely striate, 

 with the spaces between them granular, the space or groove 

 between the second and third being deeper than that between the 

 third and fourth. The first, the internal or pollical lobe, forms a 

 continuous subtriangular mass, directed obliquely backwards and 

 inwards when the pollex is drawn back, and the external moiety 

 of the carpal pad is larger than in Trichosuriis. 



The capacity for co-operative movement of the first and second 

 digits in a plane nearly at right angles to that of the third, 

 fourth, and fifth seems to have been overlooked in Fhalanger 

 maculatus. Bensley, at all events, records the similar phe- 

 nomenon in Fseitdochirus and Phascolarctos as peculiar to these 

 two genera. Nevertheless, the modification in question may be 



