1914-] ^- H. Gravely : An Account of the Oriental Passalidae. 187 



produced by friction however, that but Httle reliance can be placed on them in the 

 absence of other distinctive characters. In addition to the median groove there is 

 always a pair of marginal grooves, whose structure is often of importance. These 

 grooves are situated close to the lateral margin, and extend upwards along the anterior 

 and posterior margins, beside which, in certain species, they meet in the middle line. 

 Near the posterior angle on either side is a depression or pronotal scar , a structure 

 which is rarely of use in taxonomic work. The general surface of the pronotum is 

 either smooth or covered with punctures so small and shallow that they are quickly 

 removed by friction and are of little or no use in taxonomy; but the sides are often 

 strongly punctured especially in the neighbourhood of the scars, and of the ante- 

 rior angles. The extent of this puncturing is always subject to some variation, and 

 in certain of the species which vary greatly in size (e.g. Episphenus indicus) it is much 

 more intense in small than in large specimens; nevertheless it often affords a useful 

 confirmatory character in the diagnosis of a species. 



The prosternum, or median ventral plate of the prothorax, seems to me to be of 

 but little taxonomic importance. It consists of a median piece, which is slightly 

 expanded, in front of and behind the sockets [coxal cavities) in which the front legs are 

 inserted, to form an anterior and posterior plate, from the former of which a pair of 

 large plates {} episterna) spread outwards, each in the form of a triangle attached by 

 its apex. The median piece is often keeled in front, especially in the Aulacocychnae ; 

 but in this subfamily the posterior part of the keel is usually hidden by the project- 

 ing coxae, or basal joints of the legs. The posterior plate is pointed behind in the 

 first section of the family and broadly truncate in the second; in some species it 

 usually bears hair-carrying punctures, but the presence of these has never proved 

 to be constant. 



The plates of which the lateral parts of the underside of the prothorax are com- 

 posed are completely fused, and may be collectively referred to as the lateral plates. 

 Differences in the sculpture and pubescence of these plates afford useful confirmatory 

 characters, but they are never of any great taxonomic importance. 



Mesothorax. 



The scutellum, or median dorsal plate of the mesothorax, is partly hidden under 

 the bases of the elytra, and the triangular area exposed between them is all that need 

 be considered here. The base of the triangle forms the anterior margin and is invari- 

 ably finely striato-punctate and pilose. Whether this punctured pilose area is visible 

 depends partly on the extent to which it is developed, and this differs in different 

 individuals of a single species as much as in individuals belonging to the majority of 

 different species. It also depends on the extent to which the pronotum is drawn 

 back over the mesothorax, and the taxonomic value of this area appears to me to 

 have been greatly overrated by Kuwert. In some species other parts of the scutellum 

 are punctured as well; the position of such punctured areas appears to be of greater 

 importance than their extent. 



Below the bases of the elytra, which do not appear to be of any taxonomic 



