T9I4-] F- H. Gravely : An Account of the Orientai Passalidae. 339 



has been unable to cross the Gangetic Plain, the latter genus has had no difficulty in 

 occupying the Sunda and Philippine Islands, as well as a large part of the Asiatic 

 mainland. 



The evolution and migration of different forms of Gnaphalocneminae seems to 

 have followed lines similar to those followed by the Aceraiinae, the most primitive 

 forms again being driven out from the iVrchipelago ^in this case eastwards to Australia 

 instead of westwards towards Ceylon. As a result of this, the most closely related 

 (symmetrical) forms of the two subfamilies are found only in two widely separated 

 countries on the periphery of Indo-Australian area, the intervening' countries being 

 inhabited by more highly specialized forms most of which are asymmetrical (pp. 

 313-315). 



4. The Dominant Species. 



Five Oriental species stand out from all others on account of their extraordinary 

 variability in size. Three of these belong to the Aceraiinae, and two to the lycptau- 

 lacinae (p. 262). 



Of the first three, one {Episphenus comptoni) is confined to Ceylon, one {Epis- 

 phenus indicus) to the Indian Peninsula, and one (Aceraius grandis) to the rest of the 

 Oriental Region. Each of them differs from the species of Aceraiinae with which they 

 are geographically associated in that they are more abundant, more highly asymmetri- 

 cal, and always markedly gregarious ; but these distinctions are much less pronounced 

 in Episphenus indicus, than in the other two. Aceraius grandis, in addition to these 

 distinctions, is by far the most widely distributed member of its genus. It has 

 further been pointed out, that of the three genera of Aceraiinae inhabiting the country 

 east of the Ganges, Aceraius, which is the most markedly asymmetrical, is also the 

 most numerous both in species and in individuals ; Ophrygonius, which differs from 

 Aceraius principally in having symmetrical mandibles, comes next, and is perhaps 

 equally widely distributed ; Tiber io ides, in which the head is symmetrical as well as 

 the mandibles, being the smallest and scarcest genus of the three (pp. 311-313). 



No asymmetrical species of Leptaulacinae are known ; but there is reason to 

 suppose that the structure of the head found throughout this subfamily indicates 

 an even higher degree of specialization than does asymmetry (p. 330). It is 

 therefore not surprising to find that the two variable species, both of which are 

 gregarious, and much more abundant than any other species of the subfamily, are 

 even more widely distributed than any of the dominant species of Aceraiinae, both of 

 them being found in all subregions of the Indo-Australian area in which Passalids of 

 any kind occur. 



5. Habits. 

 Such information as I have been able to gather together concerning the habits of 

 Oriental Passalidae is recorded above under the descriptions of the several species 

 {Taeniocerus bictispis, -p. 211; Pleurarius brachyphyllus, p. 215; Tiberioides austeni, 

 pp. 216-7 ; Episphenus comptoni, pp. 219-220 ; Episphenus indicus, p. 222 ; Episphenus 

 neelgherriensis , p. 223 ; Aceraius grandis, sub-sp. hirsiitus, p. 233; Aceraius helferi, 



