122 Memoirs of the Indian Museum. [Vol. VII, 



The most primitive species of the Australian Region belong to the genus Mastochilus, 

 a genus which, like the Oriental Episphenus, contains both symmetrical and more or less 

 strongly asymmetrical species. The subgenera Pharochilus and Mastochilus, which with one 

 exception (M. pectinigera, Heller, from New Guinea) are confined to Australia, contain large 

 and robust symmetrical insects. The subgenera Analaches and Cetejus, which with one 

 exception (M. australiensis from Australia) are found in the islands north of Australia, 

 contain smaller and often slighter insects which are almost always more or less asymmetrical. 

 Of the two species of Episphenus inhabiting Ceylon the dominant one is slightly 

 asymmetrical, the other, which is symmetrical, being closely allied to it, but much less 

 abundant and of smaller size. In Australia, on the contrary, the various symmetrical 

 species are dominant, the asymmetrical Mastochilus (Analaches) australiensis being 

 comparatively rare ; which suggests that M. australiensis is a comparatively recent 

 importation and has not been derived directly from its symmetrical compatriots. This 

 suggestion is supported by the fact that M. australiensis is much more closely related to 

 Papuan than to Australian species, being indeed one of the most highly asymmetrical 

 members of its genus, and by the fact that it has been recorded from New Guinea as well 

 as from Australia. 



The genus Mastochilus probably represents the primitive stock from which the genera 

 Labienus (with Protomocoelus) , Gonatas and Pseudepisphenus (with Tarquinius) have been 

 derived. 



In Labienus specialization affects mainly the metasternum, apparently in association 

 with the wings, which tend to lose their normal function and doubtless to become more 

 efficient stridulating organs at the same time. In the most highly specialized members of 

 the genus, which appear to be confined to the Moluccas, the elytra are united in the middle 

 line, species with separate elytra being apparently to be confined to New Guinea, the 

 Aru Islands, etc. 



Protomocoelus appears to have been derived from the simpler forms of Labienus. Its 

 dentition is reduced, in which respect it is the most highly specialized of all the species 

 with a modified metasternum. But the elytra are not united nor do they show any tendency 

 to become ovate. The genus occurs in the Solomon Islands and has been recorded from the 

 Moluccas, as well as from the Islands inhabited by the simpler forms of Labienus. 



The genus Gonatas constitutes a second line of descent from Mastochilus. The 

 metasternum, wings and elytra are always normal ; but the mandibles become very 

 strongly asymmetrical, and the posterior margin of the mentum very strongly arched, in 

 highly specialized forms. The progressive stages of this development are still preserved in 

 the less highly specialized species. The most primitive species of all, G. minimus, appears 

 to be confined to New Guinea and its neighbouring islands ; but G. pumilio, the species 

 most closely allied to it, although occurring there appears to be centred in the Moluccas. 

 Much larger and more abundant than either are 67. schellongi, G. germari and 67. naviculator, 

 which must be regarded as the dominant species of the genus. 67. schellongi is somewhat 

 more primitive than either of the others, and is confined to New Guinea, the other two 

 being centred in the Moluccas, though recorded from New Guinea and from Java and the 

 Philippines also. 



