HuTTON. — 0)1 Meioiiornis. 



559 



Length of the metatarsus, 184mm. (7'25in.) ; of the tibia, 

 393mra. (15-5in.) ; and of the femur, 254mm. (lOiu.). 



Genebal Kemarks. 

 The differences thus shown to exist between the birds from 

 Glenmark and those from Kapua and Enfield are probably 

 due to differences in the age of the deposits. Geological 

 considerations would favour the idea that the Enfield deposit 

 was the youngest of the three, as the bones were close 

 to the surface, while the fact that M. casuarinus and 

 M. didinus are less differentiated from each other at Glen- 

 mark than at the other places may be taken as palaeon- 

 tological evidence that it is the oldest ; and, arranging the 

 deposits in this order, we have the average dimensions of the 

 leg-bones of the two species as follow : — 



Meionoenis casuarinus. 



Meionoenis didinus. 



On the supposition, therefore, that the three deposits of 

 bones are of the relative ages here put down, we find that 

 during the interval M. casuarimts became larger, especially in 

 the tibia and femur. In M. didimis, on the contrary, the 

 metatarsus and tibia remained practically the same,''' while 

 the femur got smaller. The two, therefore, differentiated 



'The Kapua birds, however, had a smaller tibia. 



