486 Mr. G. J. Arrow ou 



prolongation of the mesosternum, although the absence of 

 the yellow markings and the peculiar sooty band surround- 

 ing the scutoUum make it easily distinguishable. It would 

 not have been described but for the interest attaching to 

 it as demonstrating the little systematic importance in the 

 degree of development of the sternal process, which has 

 been made the occasion of generic separation. The very 

 close relationship of this species to others in which the 

 process is almost absent is strikingly evident. 



In P. hcterocera, Ohaus, which represents Dr. Ohaus' 

 8th section, the sexes differ typically by the males having 

 the elytra scarlet, sometimes with more or less black at 

 their base, whereas the female is wholly black. The 

 insects of this section are very variable, however, in 

 coloration, and Dr. Ohaus mentions an exceptional female 

 specimen with red elytra. Another in the British Museum 

 shows a trace of red, while several males are entirely black. 

 These exceptions however only indicate that the rule is 

 not invariable. There is another, and probably invariable, 

 difference in the form of the anterior horns which in the 

 male are separate and parallel and in the female converge 

 in a right angle at the base, 



P. dimidiata and nitidula of Erichson are closely related 

 to this. Dr. Ohaus mentions that all his specimens of the 

 former are females. A search for the male has revealed 

 it in Urleta ometoides of Westwood. The type of this was 

 collected by Wallace, together with two specimens of 

 dimidiata, at Singapore, and a slight comparison shows 

 them to differ only in coloration and in the cephalic 

 armature, the points by which the sexes of the previous 

 insect are distinguished. In order to confirm my opinion 

 I dissected the specimens mentioned above, which are 

 contained in the Oxford Museum, and demonstrated West- 

 wood's insect to be a male and those collected Avith it 

 females. It may bo mentioned that Westwood did not 

 recognise the latter as P. dimidiata (although he had 

 himself published the description of this in an Appendix 

 to his own Monograph), but evidently selected the more 

 conspicuous insect for description without any examination 

 of the others, and of course without any knowledge of the 

 sexual peculiarities of the genus. 



Ericlison's type, as well as the females in the Oxford 

 Museum, are black with the pygidium and the posterior 

 half of the elytra red. The male is red with the exception 



