480 Mr. Gilbert J. Arrow on Characters and Eelationships 



sliips anew, by means of the much larger materials now 

 available. 



The division of the Scarahaeidae into La.])arosticti and 

 Plcurostidi according to the situation of the spiracles, 

 although useful, does not correspond to any sharp natural 

 line of cleavage. There are not only two, but several 

 types, which pass one into the other, so that the point 

 selected for the line of division must be more or less 

 arbitrary, and if fixed with reference to this single 

 character alone may be quite unnatural. It has long 

 been recognized that the Laparostict type is normally 

 accompanied by a more primitive condition of the labium, 

 which has a free bilobed ligula, while in the Pleurosticts 

 the ligula is indistinguishable, or almost indistinguishable, 

 from the mentum. This is a test sometimes difficult to 

 apply, and of little use in the case of those genera in 

 which the organs of the mouth are partially atrophied. 

 A more obvious distinction, and one which seems to me to 

 be of some significance, is found in the conforn:iation of 

 the hinder part of the abdomen. In typical Pleurosticts 

 this is large, highly chitinous and rigid above, but in 

 Laparosticts it is less bulky, the dorsal part is scarcely 

 chitinized, and, except in the most highly specialized 

 groups (e. g. the Coprinae), not at all rigid. In all Lamel- 

 licornia the last dorsal segment is very strongly chitinized, 

 and in the Pleurostict sub-families the one preceding it is 

 closely connected with it, large, rigid and continuous at 

 the sides with the penultimate ventral segment, forming 

 a solid ring, in which the last spiracle is situated. In 

 the Laparosticts this segment is not completely rigid, or 

 if it is so is not continuous with the corresponding 

 ventral segment. 



Certain insects of peculiar conformation, the most 

 important of which are the Glaphyrinae, have been 

 attached by some system atists to one and by others to 

 the other of these great divisions. In the case of the 

 Glaphyrinae there has been a general agreement since 

 Erichson to treat them as Laparosticts, but Leconte 

 and Horn in their Coleoptera of North America com- 

 promised matters by placing a very large portion of the 

 Lamellicornia in an intermediate third division called 

 Melolonthinae, which he divided into Laparostict Mdolon- 

 thinae and Pleurostict Melolonthinae, the former consisting 

 of the Glaphyrini and another little anomalous group, the 



