Ixxxiv FAUNA HAWAIIENSIS 



three joints, the terminal one having in some aspects an appearance of forming two. The 

 mouthparts of Lit/iiirqus are, as I have pointed out, extremely unlike those of ordinary 

 Megachilidae, the tongue being extended far backwards along the breast. This species 

 nests in wooden posts, sometimes forming extensive colonies. We have seen such a 

 colony in the upright posts supporting a house in the Nuuanu valley, and others else- 

 where. The bees are very partial to the flowers of Iponwea pes-caprae and other 

 Ipomoeas. Sometimes many examples may be found asleep in these flowers, after they 

 have closed up for the day. This species is I believe of Asiatic origin. 



Pemphredonidae. — The Mimesidae, which in the systematic account I considered 

 a family, are perhaps better treated as only a sub-family of the Pemphredonidae. 



The two genera represented have I think certainly originated from one ancestral 

 immigrant form, the home of which is quite uncertain, as the genus Mimesa, to which 

 they are allied, is of wide distribution, inhabiting both the new and old worlds. 



The Hawaiian forms are easily distinguished by the great length and slenderness 

 of the basal joints of the antennal funicle, the long petiole, and the remarkable head 

 structures of the females. In the one genus these consist of a remarkable genal spine, 

 in the other of a peculiar modification of the clypeus. 



In most of the species of Ncsoniimesa the genal spines vary much in development, 

 but the form in examples, in which they are fully developed, is more or less character- 

 istic of the species. This great variability renders their specific separation difficult and 

 the males are extremely similar in all the species. In Deinoniimesa on the other hand 

 the clypeal structure does not appear to vary to any noteworthy extent, though some of 

 the species vary a good deal in other structures. 



It seems quite certain that both these peculiar structures are in some way connected 

 with the capture of their prey ; in the one case [Deino»ii)uesa) the effect is to produce a 

 kind of large spurious mouth opening, in the other [Nesomimesa) the long fringed 

 mandibles, when agape, and the pendent spines also form a sort of trap for the seizure 

 of the prey. The variation in individuals in the development of these spines is very 

 remarkable, for they are frequently extremely reduced in size. One would suppose that 

 a structure of this nature and importance would be quickly brought to a state of great 

 constancy by the operation of natural selection. On the supposition that I am correct 

 as to the use of the.se spines, and it is difficult to doubt this, the variation exhibited by 

 most of the species is very surprising. I believe the Kauai species, which is more 

 distinct from the others, than they are from one another, is nearly constant in the form 

 and development of its genal spines. 



As in the other endemic species of Aculeate Hymenoptera, occasionally one meets 

 with specimens of these insects in which the abdomen is of a reddish colour instead of 

 black, a familiar variation in many kinds of Aculeates in other countries, and apparently 

 due to the adults having preserved the coloration of immaturity. 



