DISCOGNATHUS. 189 



In the absence or the feeble development of a fold bordering the mental disk, which 

 may be very indistinct, this species differs from all its congeners. Some specimens, as 

 stated above (p. 180), approach very closely to the condition of things in the Asiatic 

 genus Crossochilus, whilst others show more agreement with the typical Discognathus. 

 The amount of variation in this respect is well shown by the large series of specimens 

 collected in Lake Zwai by Mr. Zaphiro and presented to the British Museum by 

 Mr. W. N. McMillan. 



