21. The Evolution and Distribution of certain Indo- 



Australian Passalid Coleoptera 



i 



By F. H. Gravely, M.Sa, Assistant Superintendent 



in the Indian Museum. 



(Read at the First Indian Science Congress, January Kith, 1914.) 



[With Plate XXIV.] 



In a previous paper in the Journal of this Society 2 I 

 gave a preliminary account of the taxouomic results of some 

 investigations which 1 have recently been making on the Ii.do- 

 Australian Passaiidae. In the present paper I propose to des- 

 cribe, as briefly as possible, certain facts connected with the 

 evolution and distribution of these beetles, facts which have 

 come to light as a result of the same investigations and of the 

 modifications in classification advocated in that paper. 



Of the six subfamilies of Indo-Australian Passaiidae there 

 recognized, two— the Aceraiinae and Unaphalo.neniinae— are 

 remarkable in that many of the species belonging to them 

 are more or less highly asymmetrical; and a s'udy of the dia- 

 gram on pi. XXIV, and of its explanation, will be sufficient to 

 show that the asymmetrical condition has been t volved separ- 

 ately, not only in the two subfamilies as a whole, but aLo in 

 different groups of the (Jnaphalocneminae. For it will be 

 noticed that five different types of asymmetry occur, wnicli 

 show separate lines of evolution diverging from some sym- 

 metrical or almost symmetrical ancestor. 



These five types of asymmetry may be termed the Acera- 

 tus, Protomocoelus, Gnaphdocnetms, Piestkenus and Gonatas 

 types respectively, alter the genera in which they severally 

 attain their fullest development; and each is characteristic of 

 a different group of genera, 5 capable, wita one exception, 4 of 

 complete separation one trom another on the characters afforded 

 by the mentum and antennae, as well as by those of the struc- 



l Published with the permission of the Trustees of the Indian 

 Museum. 



*■ **A preliminary account of a revised Classification of the Indo- 

 Australian Passaiidae," J.A.S.B. (N.S.), viii (1912), pp. 403-7. 



The Plestttenus group contains only one genus Piestkenus. The 

 precise relation of the genus Tortus to the other genera of the Gonatas 

 group has yet to be determined. 



Trie distinction between the Gnaphaloc nemis and Plesthenxis groups 

 rests solely on the structure of the anterior margin of the head. 



