i8o Memoirs of the Indian Museum. [Vol. II, 190g.] 



characteristic of other pediculate fish such as Halicmetus, Dibranchus and Lophius} 

 An essential character may therefore be more Hable to change than a trivial one. 



It sometimes happens that two animal forms resemble one another very closely 

 as regards their specific characters though differing in some weightier generic charac- 

 ter. Such a phenomenon is well known and is usually ascribed to "convergence," 

 — a term of uncertain value. 



It does not, however, necessarily follow that because two forms differ in a funda- 

 mental character, while resembling one another in certain specific characters, that 

 these latter have been acquired independently in the two cases ; nor does it follow 

 that the two forms must have been long separated in their descent. 



The case of Platytrodegen and Platytrodes , the case of Chaunax pidus and 

 C. apus (antea ) provide excellent illustrations of this principle. 



' I assume that the " humeral " spine of Lophius is the same structure under another name, for it 

 is based on the opercular bones, and has the same multifid form. 



