4 Memoirs of the Indian Museum. [Vol. VII, 



this additional pair of marginal tubercles is formed as a result of this tendency. Solenocyclus 

 is too closely allied to Pentalobus and Erionomus to admit of any doubt as to the identity 

 of the homologies of their cephalic tubercles. The cephalic tubercles of certain species of 

 these however, bear the closest possible resemblance to those of the Indo- Australian 

 genus Leptaulax ; and there does not appear to be any conclusive evidence to show whether 

 the homologies of Leptaulax are the same as those of Tarquinius, as previously suggested, or 

 may not really be the same as those of Erionomus. In the former case the inner and outer 

 pairs of marginal tubercles will be the true inner and outer tubercles respectively, and the 

 rudimentary tubercles sometimes formed on the frontal ridges at the point where these bend 

 forwards will be secondary structures. In the latter case these rudimentary tubercles will 

 represent the true inner tubercles, the inner pair of marginal tubercles will be the true outer 

 tubercles, and the outer pair of marginal tubercles will be secondary structures. 



It was suggested in my " Account of the Oriental Passalidae " (p. 330) that the Leptau- 

 lacinae were of comparatively recent origin, and were still spreading from some distributional 

 centre towards the middle of the Indo- Australian area, into the outlying parts of this 

 area, such as the Indian Peninsula and Ceylon. If this is so — as all available evidence 

 regarding their distribution seems to indicate — it is most unlikely that they are at all 

 closely related to any but Indo-Australian groups, a suggestion whose correctness is 

 confirmed by the fact that the anterior lower tooth in the Leptaulacinae is of a form found 

 only in Indo-Australian groups (see below, p. 9). Presumably, therefore, the origin of 

 the Leptaulacinae is to be sought among Indo-Australian forms. But there is no definite 

 evidence to show that they are in any way related to Tarquinius, the only known Indo- 

 Australian Passalid to which they bear even a superficial resemblance. The fact, moreover, 

 that in most Indo-Australian forms the outer tubercles tend to be separated by a distance 

 which is less than the width of the clypeus, makes it easy to suppose that the evolution 

 of the Leptaulacinae may have been on lines parallel to those of the evolution of Ethiopian 

 forms. 



In view of this uncertainty as to the homologies of the cephalic tubercles in the Leptau- 

 lacinae it seems best to continue to use the terms " inner " and " outer " tubercles in the 

 connection in which they were used in my previous paper ; but in addition to insert the 

 word "marginal," when speaking of the Leptaulacinae, in order to show that in this case 

 the terms are used in a descriptive sense which is not necessarily in accordance with 

 morphology. 



Flightless Species. 



In several groups of American and Indo-Australian Passalidae there are species which 

 have lost the habit of flight. This tends in all cases to produce certain modifications of 

 structure : — 



i. The union of the lateral and intermediate areas of the metastemum. 



2. The union of the elytra in the middle line. 



3. The shortening of the elytra and the rounding of all their contours. 



4. The reduction of the wings, which appear to become thereby more efficient 



stridulating organs. 



