38 
MONOTREMATA. 
base of tlie mandibles, which extends the angle of the mouth 
from the base of the lower jaw to equal the breadth of the 
base of the upper one, which must increase the facility for 
receiving the milk ejected from the mammary areola of the 
mother. 
There is very little difference in the size of the male and 
female OrnithorhyncJius ; but the males, it would appear, are 
rather the larger. The average length, in fifteen specimens, 
Mr. Bennett found to be 1 foot 7 inches to 1 foot 8 inches in 
the males, and l foot 0 to 1 foot 7 inches in the females. One 
male specimen, shot near the Murrumbidgee River, measured 
J foot 1 lj inches. The following dimensions, taken from a 
recent specimen, will give an idea of the proportions of the 
parts : — 
Inches. 
Length from the extremity of the mandible to the ex- 
tremity of the tail ... 
. 1 ft. 7i 
Length of upper mandible . 
. 2{ 
Breadth of ditto 
. 2* 
Length of lower mandible . 
. 1J 
Breadth ... ... ... ... 
. 1} 
Length of fore leg ... 
. 3J 
Breadth of fore foot expanded ... 
. 4| 
Length of tail 
. 4J 
Breadth of ditto at the broadest part ... 
. 3f 
Hind leg to extremity of longest claw 
. 4 
Breadth of hind foot 
. 2J 
The other species of Ornithorhynchus enumerated in 
Zoological works, it appears to me, are founded upon indi¬ 
viduals differing in age only. In the* largo and mature 
specimens, the fur is crisp, and of a dull brown colour; whilst 
in the smaller specimens it is of a bright brown hue, and soft 
to the touch, and, on the under parts of the body, is almost 
white. Those of smaller size and brighter colouring havo 
received the specific names, rufuH , lavis % and brevirostris; 
and I may further observe, that the specimen from which Dr. 
Shaw drew up his original account, and which is now in the 
