INTRODUCTION xcv 



Group II. 

 Identical with IV on Oahu. 

 O. niolokaiensis, sociabilis, sinithii, insiibicola, nubicola nivtcola. 



Group III. 



Insects with red thoracic or abdominal markings or both, the wings dark and with 

 blue reflections. 



O. frater, monas, cephalostictus, naiadum, tempe, dryas, potaniophilus, microdemas, 

 monobius, erythrosiactes, montivagus, sandwichiensis, petrobius, deinogaster, homoeogaster. 

 (Plate XVI, fig. 6.) 



On Hawaii there is a general tendency of the above three Maui groups to become 

 fused into one large group, all representing I. O. obscure-punctatus and riibropustu- 

 lahis and one or two others may be recognized as obscure members of Group III. 

 O. newelli, sociabilis, sco7'iaceus, represent II. 



Speaking generally of these groups, I find that in the field, the members of each 

 are easily enough distinguished. There are, as might be expected, some cases of 

 species that are intermediate in appearance and which might be placed in either of 

 two groups, but these are very few. On Kauai Group II stands out remarkably from 

 all others, since nearly all the Kauai species belong to it, while it is only approached 

 in appearance by a few species in Group IV on Oahu. The tendency of the species to 

 become red-marked on the intermediate islands is very striking, nearly half the known 

 species being so coloured. 



Group IV on Oahu ( = Group II of Maui, etc.) is not very clearly marked off from 

 its Group I, when the insects are seen in flight, but as they usually have a characteristic 

 grey or hoary appearance they may be kept apart, especially as they represent species 

 mostly peculiar to open country or open spaces in forest country. When their represen- 

 tatives on Hawaii are considered, they become much less distinct from those representing 

 Group I on that island. 



Groups II and III on Oahu are peculiar to itself, the dull red markings, clear 

 wings and body clothing of the former giving its members, dead or alive, an appearance 

 unlike anything else, while the shining fuscous wings of the latter render that group 

 equally unmistakeable. 



In a few cases, isolated species have been found on islands, where they ill accord 

 with the groups there represented, but one cannot overlook the probability of these 

 being recent immigrants. Thus O. frater, a widely distributed species, has been found 

 very rarely on Oahu, where it does not fit into any colour group, as it does on Maui, 

 where it abounds. Excepting on Kauai, the Group I of Oahu is well represented on 

 every island, besides tending to absorb all others on Hawaii, so that nearly half the 

 known species of these wasps may be referred to it. The dominance of this group 

 increases the blackness of our series, for it contains species almost or entirely black and 



