1929 ] Melissodes obliqua and Perdita opuntiae 295 
my attention to the fact and states that the paper gives 
“the impression that the bee would not be able to live within 
the stone if it were not for some crack or fault on its 
surface”. 
No doubt the misinterpretation arose from Fig. 1 which 
represented a typical nest, all of the tunnelways being in 
the same plane. The entrances to this particular nest were 
in a crack. I had chosen it for the illustration because I 
could show all the ramifications of the tunnelways in two 
dimensions. In this respect it was not a typical nest. 
The actual condition is this: Dozens of nests of Perdita 
opuntize are found in the firm stone at White Rocks, Colo- 
rado. Each nest has two or more entrances. In a small 
percent, of the nests the entrances are found in cracks or 
faults in the stone. But in the majority of the nests the 
entrances are situated in solid stone in the immediate 
vicinity of which there is not the slightest sign of a crack 
or fault. In these latter nests one finds the entrances ir- 
regularly distributed over the surface of the stone in such 
a manner that they could not be connected together by a 
crack. Also upon excavating these nests one finds that the 
tunnelways are not confined to individual planes (as would 
be the case if they were in faults) but ramify in all three 
dimensions throughout the stone. So there is no doubt that 
the bee actually nests in solid stone. 
I might mention in passing that in the original paper, 
page 75, I stated that I had found no report in the literature 
of a wasp digging its nest in stone. Since then I have 
learned from Dr. Davidson, in California, that years ago 
he had published a paper describing the habits of a wasp 
that nested in a soft sandstone. 
