1914- ] ^- H. Gravely : An Acconnt of the Oriental Passalidae. 313 



lowest terminal tooth still well developed on both mandibles and the anterior 

 angles of the head even when prominent not asymmetrical, have been driven 

 beyond the Gangetic Plain ; but one of them has developed all the characteristics of a 

 dominant form, except perhaps a higher degree of asymmetry than its allied competitor, 

 although this competitor is still quite common. In the genera Ophrygonius and 

 Aceraius, which inhabit the Oriental Region west of the Bay of Bengal, Aceraius 

 grandis has alone developed all the characteristics of a dominant form. It is more 

 abundant than any other species of either genus; its distribution is wider; and, 

 with the exception of A. occulidens, it is structurally the most highly specialized 

 member of the whole subfamily. It seems likely, moreover, to be the progenitor 

 of two species, now apparently in course of evolution, one in the south and the other 

 in the north, to which the names A. grandis, s. str. (with rectidens as a variety) 

 and A. grandis sub-sp. hirsutus, have respectively been applied above. 



The genus Aceraius is so completely united by transitional forms to the genus 

 Ophrygonius , as to render its origin therefrom almost certain. In Ophrygonius, 

 although the anterior margin of the head is asymmetrical the mandibles are sym- 

 metrical; whereas in all except a few (transitional) species of the genus Aceraius, the 

 mandibles are also markedly asymmetrical ; so it is quite in keeping with what has been 

 said above of the great abundance of the most highly specialized species found in 

 different parts of the Oriental Region, to find that the genus Aceraius is much more 

 abundant than the genus Ophrygonius both- as regards individuals and number of 

 species; and that the somewhat isolated and symmetrical genus Tiberioides, which 

 occurs only in the northern portion of the area inhabited by these genera, is less 

 abundant than either. Many of these facts are illustrated and compared with similar 

 ones relating to the Gnapholocneminae in text-fig. 7 (p. 314). 



Although Palk Strait and the Gangetic Plain appear to have influenced the dis- 

 tribution of the Aceraiinae in a much more striking manner than has the line separat- 

 ing continental Asia from the East Indian Archipelago (including the Malay Penin- 

 sula), the influence of this line can also be seen. Aceraius grandis is the only species of 

 the subfamily found on both sides of this line. The northern and southern races of 

 this species occur one on each side of this line towards the west ; but further east the 

 northern race has established itself not only in Hainan and Formosa, but also in 

 the Philippine Islands, whose fauna should presumably be allied rather to that of 

 the Archipelago, and from which two representatives of this fauna — Aceraius laevicollis 

 and Aceraius horneanus — have already been recorded. 



The Gnaphalocneminae, most of which are asymmetrical, appear to hold much the 

 same position in the fauna ofthe islands east of the Straits of Macassar as the Aceraiinae 

 do in the countries west of it. But this zoogeographical boundary has not offered 

 the same difficulties to their migration , as it has to that of the Aceraiinae ; for one 

 whole group of Gnaphalocneminae is found in, and perhaps confined to, the Oriental 

 Region ; and at least one species of the genus Gonatas occurs in the Sunda Islands.' 



' G. german and wßW7CM/fl/or have been recorded; but all the specimens I have seen labelled with 

 either of these names appear to me to belong to a single species. 



