682 Mr. R. C. L. Perkins on the 



" The species fall into three very distinct structural 

 groups: — (1) 0. oahuensis: isolated structurally and in 

 habits : common in all suitable localities, but less so than 

 0. pseudochromus : affinity with other Hawaiian Odynerus 

 is not clear, but requires far more study ; (2) 0. pseudo- 

 chromus, pseudochromoides, leiodemas : allied species, the 

 first two ubiquitous and common in their proper localities : 

 the third is probably generally to be found with them, but 

 is much less numerous ; (3) 0. cucharis, homoeophancs : 

 allied species, of which one is found with species of the 

 structural group (2) in some localities, the other with them 

 in other localities. They are probably always relatively 

 rare." Nov. loth, 1911. 



Group IV. Insects with usually two pale abdominal 

 bands, the wings more or less infuscate and with blue 

 reflections, body generally with pale tomentum. 



0. xerophilus, nautarum, de Sauss., acoelogaster ; Pseudo- 

 pterocheilus relictus* 



* [I was particularly anxious to see the members of Colour-groups 

 which had been captured at the same time and place, in order to be 

 able to estimate the relative numbers and obtain conclusive evidence 

 as to the predominant species. Dr. Perkins very kindly collected 

 for me on three occasions the specimens which are tabulated in the 

 following extract from his letter, written May 20th, 1912, from 

 Honolulu. The captures of each date are kept together in the Hope 

 Department, where they may be studied at any time. They were 

 exhibited, in illustration of Dr. Perkins' paper, at the Second 

 Entomological Congress at Oxford during the past summer.] 



I have been out in the country on three occasions lately to catch 

 Odynerus, and had Kershaw to help me. It is a bad season on the 

 lowlands, as we have had no winter rains and the country most 

 favourable for Hymenoptera is parched up. It is interesting to see 

 what is dominant under these conditions. 



On the first day (April 26th, 1912, Makiki, Oahu, below 400 ft.) 

 caught only one species, 0. nigripennis (38 specimens), but I saw 

 one individual either of Nesodynerus rudolphi or Od. montanus. 



On the second day (May 3rd, lowlands near coast, east of Honolulu) 

 we caught of the same all-black, blue- winged Group I : — 



0. nigripennis (21) ~| 



O. montanus (1) I 3 structural groups in these 4 



0. iopteryx (2) J species ! 



Nesodynerus rudolphi (6) J 



Of the white-banded Group IV :— 

 0. acoelogaster (10). 

 O. nautarum (1). 

 Ps. relictus (1). 



