628 Mr. D. Sharp and Mr. F. Muir on the Comparative 



th( se are three, viz. Passalidae, Lucanidae, Scarabaeidae. 

 We will return to this point after touching on the 

 peculiarities of the group. 



The first of these is that in the enormous majority of 

 the forms there is a great reduction of the scleritic parts 

 of the median lobe. If the characters of a Lucanid and 

 a Scarabaeid be examined, it would at first be supposed 

 that but little real affinity exists between the two. On 

 the other hand, if Trox (usually placed in Scarabaeidae) 

 be added to the compared material, the difficulty becomes 

 that of separating the two divisions, for Trox agrees better 

 with Lucanidae than it does with Scarabaeidae. Trox is 

 not only very important in this respect, but also because 

 it throws some light on the very peculiar male structures 

 of the Passalidae. 



The Scarabaeidae, while exhibiting a reduction of the 

 scleritic parts of the median lobe, display an enormous 

 development of the basal-piece, which forms the "tambour" 

 (Straus-Durckheim) of the organ. This tambour usually 

 shows a constriction wliich might at first sight be supposed 

 to separate it into two parts, in which case the proximal 

 part only would be taken as the basal-piece, and the 

 distal portion might be supposed to be part of the 

 median lobe. This, however, is a most superficial obser- 

 vation ; the constriction in question merely marks the 

 attachment of the connecting membrane, the two portions of 

 the tambour being one enormous basal-piece. The lateral 

 lobes are most remarkable and are very diverse. They 

 form what is usually, in this division, called the forceps. 

 In some cases they are separate, not amalgamated, at 

 their bases {Sfilota, etc.); in another condition they are 

 amalgamated on the dorsal aspect, forming an undivided 

 piece (Felidnota) ; while a third condition exists in 

 Lomaptera (Cetoniinae), where the amalgamation of the 

 lobes occurs on the ventral aspect. In Ischiopsopha by 

 a modification of this they form a complete scleritic ring, 

 as they do in Xylotrwpes. The ventral surface of the basal- 

 piece is usually membranous for a large area, but in some 

 forms there is a chitinisation of this surface, to which we 

 have applied a special name, the ventral-piece (fig. 19, 

 t;p). In some cases this ventral-piece becomes quite 

 chitinously continuous with the lateral lobes {Xylotrupes 

 e.g.), forming thus a very large irregularly shaped 

 sclerite. 



