202 Journal of the Asiatic Society of Bengal [June, 1914 



tures (the mandibles and the anterior margin of the head) which 



are apt to be asymmetrical. 



It is evident, therefore, that the degree of asymmetry 

 which any species exhibits cannot be regarded as an indication 

 of affinity to asymmetrical species of another type ; but that 

 it is to be regarded rather as an indication of the degree of 

 specialization which has been attained. 



The Aceraiinae are found in the Oriental Region only ; and 

 this Region may be divided, with reference to them, into three 

 principal parts— Ceylon, the Indian Peninsula, and the countries 

 east of the mouths of the Ganges, including the Eastern Hima- 

 layas and everything south and east of them as far as the 

 Straits of Macassar. Not a single species belonging to this 

 subfamily is found in more than one of these tracts; and in 

 the tracts between them l no Passalids of any kind are known 

 to exist. 



In the countries between the mouths of the Ganges and 

 Straits of Macassar, three genera are found. One of these 

 (Tiberioides) is symmetrical and includes only three species, 

 none of them very common, and all practically confined to the 

 Eastern Himalayas and the Naga Hills. Both the others are 

 highly asymmetrical, and so complete a series of transitional 

 forms exists between them as to leave no room for doubt that 

 one has been derived directly from the other. Both these genera 

 are larger as regards number of species, more plentiful, and 

 more widely distributed than the first mentioned ; and one of 

 them {Aceraius), in which alone the mandibles are asymmetrical 

 as well as the anterior margin of the head, is much larger, more 

 plentiful, and perhaps more widely distributed, than the other 

 (Ophrygonius) . Further, one species of the former of these two 

 genera stands out from all others of both genera by reason of its 

 extraordinary asymmetry, its abundance, its occurrence over 

 the whole of the area they inhabit, its gregarious habits,* and 

 its variable dimensions— which are often as great as if aot 

 greater than those of any other species of the genus. It is quite 

 evident that at present this species, Aceraius grandis, is the 

 dominant species of the subfamily all over the countries east ol 

 the mouths of the Ganges. 



Similar characteristics distinguish the dominant species 

 of the Indian Peninsula and Ceylon respectively from the 

 other species of Aceraiinae living there. Only two species 

 of Aceraiinae are found in each of these areas. In the Indian 

 Peninsula the two are almost equally asymmetrical and almo st 



» i.e. (1) the Gangetic Plain, and (2) probably the dry low country be- 

 tween the hills of S. India and Ceylon, as well as the Straits between thena. 



* Of very few other species of the genus are the habits yet definite } 

 known and I suspect that a few of them will prove to be gregarious m 

 some degree. 



