1914-] F- H. GRAVEI.Y : An Account of the Oriental Passalidae. 199 



appear to me to be much more natural than a group containing all the genera 

 with reduced dentition would be. In the accompanying diagrammatic representa- 

 tion of the grouping of the genera of Gnaphalocneminae that appears to me 

 to be most natural (see previous page), the names of the genera so characterised 

 are marked with an asterisk ; and it will be seen that they appear in two different 

 places/ 



When thus arranged the genera fall into six groups (each enclosed, in the diagram, 

 by a dotted line), and it will be convenient to refer to these groups respectively as 

 the Kaupioloides , Protomocoelus, Hyperplesthenus , Gnaphalocnemis , Plesthenus and 

 Gonatas groups. The diagram indicates only the general course of the evolution of 

 asymmetrical forms with reduced dentition, from symmetrical ones with complete 

 dentition, as this is illustrated by the genera now in existence. Many of the genera 

 in the lower parts of the diagram are distinguished from those above, as well as from 

 those below them, by characteristics peculiar to themselves ; and the diagram must 

 not be taken to imply the actual descent of one genus from another now existing, but 

 only from one the general characteristics of whose head and mandibles were very 

 similar.^ 



The Kaupioloides group appears to be the most primitive, and as its members 

 closely resemble those of the subfamily Macrolininae, it may be supposed that the 

 two originated from a common stock, and have not departed very widely therefrom 

 in general appearance. The Protomocoelus group, in spite of its possession of 

 primary scars, appears to be related more closely than any other to the sub-family 

 Aceraiinae. The affinities of the two remaining subfamilies of the second section 

 of Oriental Passalidae, the Pleurariinae and Leptaulacinae, are more obscure ; but 

 it seems likely that the former is related to the Aceraiinae. 

 The genera of Gnaphalocneminae may be defined thus : — 

 ' Primary scars almost always present ^ ; when absent, area between 

 anterior part of left supra orbital ridge, and ridge joining left inner 

 and outer tubercles, deeply excavate, the excavation bounded 

 I behind by a sharply defined ridge ; dentition of right mandible never 

 '"^ more reduced than that of left , . . . . . . . . . . . 2. 



Primary scars never present ; surface of head without deep or 

 sharply defined anterior depressions, or dentition of right mandible 

 ^more reduced than that of left . . . . . . . . . . . . 9. 



' I follow Zang (19056, p. 227) in supposing the lateral and intermediate areas of the metasternum 

 to be fused in the genus Pe/o/)îWfs ; but Zang himself had not seen a specimen (1905«, p. 316). See 

 also following footnote. 



* It is, for instance, very possible that Protomocoelus and Pelopides have sprung more directly than 

 is here indicated from Kaupiolides, which they resemble in the structure of the metasternum more tha ' 

 they do Analaches-Cetejus. 



^ Perhaps always; but in the most highly specialized forms they are often very small and obscure. 

 In all the more highly specialized forms, and also in some les; highly specialized, the excavation behind 

 the anterior margin of the head is present on the left and often on both sides; and in these forms it 

 supplies an excellent mark of recognition; it faces more upwards and less forwards, and when well 

 developed is much deeper than the somewhat similar hollow often found in the genus Gnaphalocnemis , 



