1918.] F. H. Gravely : Passalidae of the World. 121 



species of the genus. 1 The genus Pleurarius appears entirely to replace Macrolinus in the 

 Indian Peninsula. This genus has otherwise been recorded only from Sumatra, whence 

 it was originally described. In the absence of further records from that island I am 

 inclined to doubt the validity of the record and to believe the genus to be confined to the 

 Indian Peninsula. If this is so the genus probably contains one species only, a species 

 whose elytra are united. Other groups of Macrolinus occupy respectively (i) the 

 Indo-Chinese Sub-Region, (2) the Malayan Sub-Region and (3) Celebes, except that one 

 rare Cebelean species belongs to the Malayan group. Species of Macrolinus with fused 

 elytra are known only in the Ceylonese and Celebean groups. 



The second series of genera of Macrolininae (PI. I) is found throughout the Indo- Aus- 

 tralian area and is remarkable for the pronounced asymmetry which is developed in most of 

 its more highly specialized members. It comprises the Aceraiinae and Gnaphalocneminae of" 

 my previous papers, one of which was devoted to a special study of its distribution ( 19 146). 



The study of more extensive material fully confirms the geographical separation, in 

 Ceylon and Australia respectively, of the primitive and closely related symmetrical forms 

 by the more highly specialized and less closely related descendants of each ; but shows that 

 I was mistaken in confusing the Celebean Passalid fauna with the Papuan, and that my 

 suggestions regarding phylogeny can be improved upon. 



Concerning the distribution of the genera Episphenus, Ophrygonius and Aceraius there 

 is nothing fresh to add. The first named is confined to the Indian Peninsula and Cevlon, 

 the two last to the rest of the Oriental Region. The species inhabiting Ceylon are less 

 highly specialized than those inhabiting the Indian Peninsula, which in their turn are less 

 highly specialized than those found on the other side of the Ganges, taking these as a whole. 

 And in each of these areas the most asymmetrical {i.e., the most highly specialized) is also 

 the most abundant, the most variable, and among the largest. It also has gregarious 

 habits (Gravely, 19146, pp. 202-204 ; 1914c, pp. 311-313). 



Similarly, in the genus Pelopides, the most abundant species in the Sunda Islands are 

 large and highly asymmetrical (P. tridens, etc.) ; but in the Malay Peninsula the most 

 abundant species (P. dorsalis) is smaller and more nearly symmetrical. The most symme- 

 trical species of all appears to be confined to Borneo, the island where a primitive form 

 would be least expected ; but it does not seem to be common there. 



The genus Pelopides is found all over the Malayan Sub-Region, and extends beyond 

 it into the extreme south of Burma, but no further. Its connection with simpler genera 

 is obscure, but it would be quite in keeping with the general relationship between the 

 evolution and distribution of asymmetrical Passalids for some ancestral form to be found in 

 Continental Asia. It seems to me possible that such may be represented in the genus 

 Tiberioides, a symmetrical genus whose presence in the area occupied by Ophrygonius and 

 Aceraius does not accord well with any direct relationship with them. If this is the case, 

 the grooves on the mentum of T. borealis no doubt represent an early stage in the 

 development of the large secondary scars found in all species of Pelopides. Closely allied 

 to Pelopides is the genus Plesthenus, which is confined to Celebes (see above, p. 96). 



1 For the distinctive characters of the several local groups of species of Macrolinus see sections 1-3 of the table on 

 pp. 82 84 above. 



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