254 
BRITISH BEES. 
bees whose parasitism is directed exclusively upwards 
in the scientific arrangement; the parasitism of all the 
rest of the genera of Nudipedes bears upon the genera 
below them in the series. Some of the species of the 
Nomadce attack more than one species or one genus, 
but the majority are strictly limited to but one genus 
and one species. The genera obnoxious to this annoy¬ 
ance are Andrena, Halictus, Panurgus, and Eucera ; the 
latter two have but one of these enemies each, the No- 
mada Fabriciana infesting the Panurgus Banksianus, 
and the N. sexfasciata frequenting the Eucera longicornis. 
Under Panurgus I have alluded to the relative abun¬ 
dance of the parasite at the metropolis of its sitos. As 
far as known, the other species are thus distributed. 
Those frequenting several indifferently are the Nomada 
alternata, Lathburiana, succincta, and rufcornis, which 
are found to infest Andrena Trimmer ana, tibialis, Afze- 
liella, and fulva, without displaying any choice ; whereas 
others confine themselves to one sitos exclusively: thus 
Nomada ochrostoma limits itself to Andrena labialis; 
N. Germanica to A. fulvescens; N. lateralis to A. Ion- 
gipes ; N. baccata to A. argent at a; N. borealis to A. 
Clarkella ; N. Fabriciana to Panurgus Banksianus; and 
N. sexfasciata to Eucera longicornis. Observation has 
not yet fully determined whither each species of Nomada 
conveys its parasitism ; several infest the Halicti , espe¬ 
cially the smaller species; the association of these it is 
difficult to determine; I have usually found several 
of the small Halicti burrowing together in the vertical 
surface of an enclosure bank, and several of the small 
Nomada hovering cautiously opposite, now alighting and 
entering a burrow, then retreating backwards and wing¬ 
ing oft. I lost patience in endeavouring to combine the 
