I9I4-] F. H. GraveIvY : Alt Account of the Oriental Passalidae. 265 



In the Passalidae, as in the lyucanidae, variation in certain structural characters 

 is found to be more or less closely correlated with variation in size. The mandibles 

 of a Passalid never attain anything approaching the remarkable development of 

 those of a male Lucanid except in the genus Ceracupes, the species of which are not 

 known to vary greatly in size ; yet in two of the most variable Passalids — A ceraius 

 grandis sub-sp. hirsutus and Leptaulax dentatus (? s. str. only)— their dentition is less 

 complex in small than in large specimens. In the former the upper tooth of the left 

 mandible is often double in very large specimens (fig. 2Sa), but not in medium sized 

 (fig. 28), or small ones ; and in the latter, the anterior lower tooth of the left mandible 

 is tridentate in large specimens (fig. 52) and bidentate (sometimes scarcely more than 

 unidentate) in small ones (fig. 52^). 



The processes of the anterior margin of the head on the other hand tend to be 

 more acute, and often proportionally longer, in small specimens than in large ones, 

 when any such differences are found. This is best seen in the processes developed 

 from the anterior angles of the head in Episphenus indicus and Aceraius grandis 

 (? sub-sp. hirsutus only) as will be seen on comparing fig. 20 with fig. 20b and 

 fig. 28 with fig. 28a. A somewhat similar phenomenon is found among I^ucanidae in 

 the genus Aegus. In large specimens of certain species of this genus (e.g. A . kandyensis 

 and A. roepstorfi) the front of the head bears two median protuberances, one above 

 the other; while in smaller specimens of the same species, although the uppermost of 

 these disappears, the lower one is represented by a pair or minute tubercles, situated 

 side by side and more distinctly separated one from another the smaller the specimen is. 



The relative extent of the punctured areas of large and small specimens presents, 

 however, a much better instance of the similarity between the variations in structure 

 associated with variations in size, found in the two families. In both families it 

 seems to be always the small specimens that are most extensively punctured, in 

 species in which any such difference occurs. In the I^ucanidae (e.g. certain 

 Himalayan species of Dorcinae) the difference is most marked in the elytra, and after 

 that in the pronotum and sometimes the abdominal sterna. In the Passalidae the 

 elytra are always furrowed, and such slight variations as occur in the extent to which 

 the furrows are punctured, do not appear to be in any way correlated with variations 

 in the size of the insect, nor does the puncturing of the lateral ribs of the elytra of 

 Aceraius grandis appear to be so correlated ; but in Episphenus indicus ana Leptaulax 

 bicolor (s. str. and to a less extent var. vicinus as well), the pronotum is more extensively 

 punctured in small than in large specimens ; and in Leptaulax bicolor the punctured 

 areas of the abdominal sterna are commonly more extensive in small specimens than 

 in large ones. 



6. THE GEOGRAPHICAlv DISTRIBUTION AND SYNONYMY OF THE 

 SPECIES OF PASSAUDAE BELONGING TO GENERA FOUND IN 



THE ORIENTAL REGION. 

 The principal difficulty in drawing up this Hst has been the working out of the 

 synonymy which it has involved. An attempt to discuss the distribution of Oriental 



