HYMENOPTERA 5 



that he examined to several of his groups of American Odynej'us, whereas after an 

 examination of the complete series of species described in this work, it appears that these 

 are in reality intimately related to one another. As a matter of fact the Aculeata are a 

 group but ill-adapted for throwing any light on the derivation of the Hawaiian fauna. 

 Odynerus, the most numerous in species of this group, is a genus almost ubiquitous over 

 the world, with vast numbers of species described, and no doubt vast numbers still 

 uncollected. Although these display an extraordinary diversity of form and appearance, 

 they have so far defied any satisfactory classification. The Crabronidae are almost as 

 unsatisfactory, and have been certainly still less completely collected. Nevertheless the 

 fact that the Hawaiian species all belong to one of the sections, in which the males are 

 remarkable for their 12-jointed antennae, will no doubt greatly aid ultimately in deciding 

 their affinities. The Mimesidae likewise are a widely distributed groujs of obscure 

 insects, but little collected. The bees of the genus Prosopis, from which I have now 

 dissociated the Hawaiian species under a new generic name, are of world-wide distribu- 

 tion, and are peculiarly difficult to study, and certainly great numbers of existing species 

 are still unknown. The structure of the terminal (concealed) abdominal segments of 

 the male is of paramount importance in this group, yet they have been entirely ignored 

 in the majority of species described. These structures in the Hawaiian species are very 

 distinctive, and differ greatly from such American and European Prosopis as I have been 

 able to dissect, and I suspect that the affinities of Nesoprosopis will prove to be rather 

 with the species of Prosopis found in New Zealand or Australia than with the others. 



So far as one can judge from a study of the relationship of the endemic species to 

 one another, all the Mimesidae, Crabronidae, Eumenidae, and the Bees of the genus 

 Nesoprosopis could have been evolved from four species which reached the islands at 

 some very remote period, one of the four species of course representing each group. 

 The total absence of any representative of so many groups of the Aculeata, certainly not 

 less fitted to pass over the great distances between the islands and other lands, and for 

 which the country is admirably adapted, is a point greatly in favour of the view that the 

 numerous species of each of the families represented arose from a single immigrant 

 species, and the examination of the structures of the species themselves greatly supports 

 this view. How rarely an immigrant can have arrived from without, can be judged 

 from the great number of species which fail to cross the short distances between the 

 islands themselves. 



In the fragmentary condition of their Hymenopterous fauna the Hawaiian islands 

 considerably resemble New Zealand, but in the case of the latter country it is less 

 extreme. At the present time the Aculeata of New Zealand have been too much 

 neglected to make any detailed comparison of value, but few species of this group 

 having been collected there. 



An important fact in connection with the Hawaiian species is their variability. 

 This is most noticeable in the Bees, Crabronidae, and Mimesidae, a great many of the 



