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



The Passalid fauna of the Moluccas is closely allied to that of New Guinea, and several 

 species have been recorded as common to both. In the genus Gonatas, however, it is 

 noteworthy that of the two species with most primitive mentum the one with complete 

 dentition is only known from New Guinea ; while of the three common species with more 

 highly specialized mentum the one with the most primitive dentition seems to be confined 

 to New Guinea and the other two to the Moluccas. Similarly, in the genus Labienus, 

 species with normal elytra appear to be confined to New Guinea and those with fused elytra 

 to the Moluccas. The allied Protomocoelus, in which the mandibles are modified instead 

 of the elytra, belongs however to New Guinea, and, although it is undoubtedly more 

 widely distributed than any of its allies, the single record of its occurrence in the Moluccas 

 should be confirmed before it is finally accepted. Pseudepisphenus and Tarquinius are only 

 known from New Guinea. 



The information at present available regarding the distribution of American and 

 Ethiopian Passalidae is much less satisfactory than that regarding the Indo-Australian 

 subfamilies. The probable distinctness of the American and Ethiopian Passalid faunas, in 

 spite of several records to the contrary, has already been dealt with (above, pp. 10- 1 1 ). It 

 is perhaps worthy of note here that no Ethiopian Passalidae are known to have the elytra 

 united, and that in America, although species with fused elytra attain the largest size, the 

 commonest and most widely distributed species have separate elytra. Among the 

 Pseudacanthinae Popilius comutus is the largest and most highly specialized of the species 

 with separate elytra and is the commonest and most widely distributed species in the 

 subfamily. Among the Proculinae no species appears to be exceptionally abundant. Among 

 the Passalinae Paxillus leachii, Passalus inter stitialis and Passalus interruptus are particularly 

 abundant and widely distributed. The last named is probably the most abundant and 

 widely distributed of all, and is also extremely variable. The group of species to which it 

 belongs appears to me to be the culminating point of the general trend of evolution through- 

 out its genus, a genus whose wealth of closely interrelated species suggests that it bears the 

 , same kind of relation to the rest of the American Passalid fauna as Leptaulax does to the rest 

 of the Indo-Australian. 



SUMMAKY. 



i. External Morphology. 



The clypeus is exposed and separated by a suture from the frons only in the subfamily 

 Pseudacanthinae. In a few other genera, mostly American, it is exposed but united 

 to the frons. In the majority of Passalids the whole of the upper surface of the anterior 

 part of the head, between the supra-orbital ridges and in front of the frontal ridges, is frons, 

 the whole of the clypeus being doubled beneath this out of sight (pp. 1-3, fig. i, 1-4). 



It is uncertain whether the inner and outer marginal tubercles of the Leptaulacinae 

 are homologous with the inner and outer tubercles respectively of other Passalidae 



(PP- 3"4)- 



The dentition is reduced only in somewhat highly specialized forms. In American 



subfamilies it seems to be associated with the loss of the habit of flight, and to come about 



