1918.] F. H. Gravely : Passalidae of the World. 77 



whenever asymmetry occurs in the mandibles, the dentition is reduced chiefly on the right 



side. 



The distinctive characters of the first four of these genera do not appear to me to have 



more than specific significance, and I propose to unite them under the name Pelopides. 



The fifth genus, Plesthenus. seems to be distinct. It is possible (see below, p. 121) that 



these genera may have been derived from Tiber ioides, but as this is by no means 



certain I have not placed Tiberioides beside them, but have left it next to the symmetrical 



species of Episphenus. 



PharocJiilus, Episphenoides, Mastochilus, Analaches and Cetejus may likewise be united, 

 the scars on the mentum, with the aid of which they have hitherto been defined, being 

 variable and not sharply distinctive. The somewhat large genus resulting from this union 

 is, however, composed of four more or less distinct groups of species, for which four of 

 the above names may be retained in a subgeneric capacity. Thus PharocJiilus may be 

 defined so as to include only large Australian species with extremely short antennal 

 lamellae and more or less extensive matt lateral borders to the mentum. And Episphenoides 

 may advantageously, T think, be re-united with the very few known species of Mastochilus, 

 and may then be defined so as to include the remaining large symmetrical species. 

 Analaches and Cetejus are very difficult to separate from Mastochilus on structural 

 grounds, but contain species of a much smaller size, many of which are distinctly 

 asymmetrical. Analaches contains somewhat larger and flatter species than Cetejus 

 with distinctly longer antennal lamellae. According to Heller, who has examined Zang's 

 material (1910, pp. 14 and 21), the upper edge of the left mandible is toothed near the base, 

 and this is in agreement with my observations on the few species before me. This tooth 

 is sometimes, however, situated so near to the base as to be hidden beneath the anterior 

 angles of the head. This is so, for instance, in Stoliczka's australiensis, which Heller 

 places in the genus Cetejus, in spite of its flattened form and long antennal lamellae, but 

 which dissection shows to be an Analaches. 



Mastochilus (s. lat.) appears to represent the simpler stock from which the remaining 

 genera, all more highly specialized, have been derived. All these other genera are found 

 mainly in the islands east of Celebes, and whenever their dentition is reduced this occurs 

 most markedly on the left side, instead of on the right as in Oriental groups (see pi. I). 



Kaupioloides, Hyperplesthenus, Aurelius, Labienus and Kaupiolus all have symmetrical 

 mandibles with complete dentition. In the most highly specialized species the elytra are 

 united, and in all of them the intermediate and lateral areas of the metasternum are fused, 

 a fusion which is closely associated with the union of the elytra, tending to follow it in the 

 other groups of Passalidae in which it occurs. Probably, therefore, these genera are losing, 

 if they have not already lost, the power (or at least the habit), of flight, the wings doubtless 

 becoming more efficient stridulatory structures at the same time. None of these genera 

 are very large, and they may advantageously be united under the name Labienus. 



and in Kaup's original description of quadricornis (loc. cit.) the only locality referred to is that of the type of lottinii, 

 a locality which he has quoted in his monograph, perhaps inadvertently, as that of quadricornis. Even if the type of 

 quadricornis should prove, on re-examination, to be labelled " New Holland " I should still doubt the validity of the 

 record, in view of the extreme improbability of any such highly specialized species, with Oriental rather than Papuan 

 affinities, occurring there. 



