338 Memoirs of the Indian Museum. [Voi.. Ill, 



Tarquini^ls, from an asymmetrical ancestor allied to the Gnaphalocneminae, suggests 

 that the union of the inner tubercles with the anterior margin of the head indicates 

 an even higher degree of specialization than does the asymmetrical condition (p. 330). 



3. Geographical distribution. 



The material examined during the preparation of this paper does not enable me 

 to discuss the relation borne by Indo- Australian Passalidae to members of the family 

 found in Africa or America; but it seems by no means improbable, from Kuwert' s 

 account of the family, that all the seven subfamilies described, with the possible ex- 

 ception of the lycptaulacinae, will prove to be confined to the Indo- Australian Region, 

 China and Japan (p. 194). 



With the exception of the Pleurariinae, Aceraiinae and Tarquiniinae all these 

 subfamilies occur on both sides of the Straits of Macassar, but the Aulacocychnae and 

 Gnaphalocneminae are much more strongly represented east of these straits, and in the 

 eastern parts of the Oriental Region, than they are further west ; while with the 

 Macrolininae the reverse is the case (pp. 311 & 313). 



The discontinuous distribution of the genus Aulacocyclas suggests that the 

 Aulacocyclinae were once more abundant towards the west than they are now. 

 Although the Macrolininae are well represented in Ceylon, they appear to be absent 

 from the Indian Peninsula. The Pleurarariinae occur only in the Indian Peninsula 

 and Sumatra, which discontinuous distribution suggests that they are probably the 

 remnants of a once more extensive group. The Leptaulacinae are centred in the East 

 Indian Archipelago. Only the dominant species seem to have established themselves 

 in India and Ceylon, and these are less common there than elsewhere (p. 311). 



The distribution of the Aceraiinae and Gnaphalocneminae, the two subfamilies in 

 which asymmetrical species are found, is of much greater general interest. It appears 

 to have been greatly influenced by the following zoogeographical boundaries: — 

 Palk Strait, the Gangetic Plain (in which Passalids seem unable to live — pp. 310-1) 

 the Straits of Macassar, and Torres Strait. Of these the Straits of Macassar are by 

 far the most important, for no group of either subfamily is found in any abundance 

 on more than one side of them. It is therefore somewhat surprising to find that this 

 is the only one of the above-mentioned boundaries, which any species of these sub- 

 families has succeeded in crossing (pp. 313 & 315-6). Another boundary of some 

 importance is that separating the East Indian Archipelago — including the Malay 

 Peninsula and presumably also the Philippines — from continental Asia (p. 313). 



The occurrence of different degrees of asymmetry in different species of Aceraiinae 

 probably affords an index to the degrees of specialization to which they have severally 

 attained, and its correlation with locality is very evident. It is concluded that 

 a migration has taken place westwards towards the head of the Bay of Bengal and 

 then south-westwards towards Ceylon, the less specialized forms being constantly 

 displaced by their more speciaHzed allies (pp. 311-314). It may further be pointed 

 out that although neither of the two most highly asymmetrical species of the genus 

 Episphenus have been able to cross over from India to Ceylon, and the genus Aceraius 



