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XVI. On Sexual Dimorphism in the Rutelid genus Parastasia, 

 ^oith descriptions of new species. By Gilbert J. 

 Arrow, F.E.S. 



[Read October 4th, 1899.] 



Plate XVIL 



In a paper dealing with tlie Anomala group of Rutelidae 

 recently published in the Transactions of the Entomological 

 Society, I pointed out the importance in systematic work 

 of ascertaining what characters were sexual. A study of 

 the Asiatic Rutelidse constituting the Parastasia group 

 has strongly emphasised this necessity and shown the 

 worthlessness, in the present family at least, of much of 

 the work in which this point has been neglected. 



Having made a preliminary separation of the specimens 

 of Parastasia in the British Museum collection upon the 

 basis of Westwood's Monograph of the genus, I was 

 surprised to find an almost entire absence of external 

 sexual differences, and dissection proved that this was due 

 to the fact that the greater number of the apparent species 

 consisted of one sex only. I afterwards found that the 

 existence of sexual dimorphism in this genus had already 

 been noticed by Dr. Ohaus in a recent paper in the Stett. 

 Ent. Zeit. As however this author has not fully recognised 

 the extent of the dimorphism, and as I have been able to 

 examine a number of types unknown to him and a large 

 number of specimens of new and old species, several 

 collections having been kindly lent me for the investiga- 

 tion of this interesting phenomenon, I have thought it 

 desirable to collect together all the instances I have been 

 able to discover, including those already pointed out by 

 him. I shall adhere as far as possible to Dr. Ohaus' 

 subdivisions of the genus. 



This group of Rutelidse includes several remarkable 

 genera, such as Peperonota, Fruhstorferia and Didrepane~ 

 phorus, characterised by extraordinary differences between 

 the sexes, and it is interesting to find the well-known 

 predominant genus exhibiting the same phenomenon, so 

 long unexpected, in many different ways. 



TRANS. ENT. SOC. LOND. 1809. — PART IV. (DEC.) 



