UTAH ACADEMY OF SCIENCES 19 
spiral of the shell. The larger females rest in the outer 
coils until settled warm weather in May calls them to 
nest building. Ata place in the spiral where the diameter 
narrows to about one-fourth inch, the bee places a thin 
partition of vegetable matter, just thick enough to hold 
the pollen in place. About three cells are then con- 
structed with their long axes following that of the spiral. 
Each cell is formed by the two partitions and is well 
supplied with pollen. By this time the mother bee has 
reached a place where the diameter has increased to 
one-half inch and she then places the cells across the 
lumen of the spiral. The opening into the shell is then 
closed by a plug of chewed plant fibres nearly half an 
inch thick. This differs from the plugs made by some 
members of the genus in that it is composed of a solid 
mass and is not made up of several layers or discs. 
This partition is placed more than half way around the 
first spiral so that the shell appears empty unless broken 
into. As a further safeguard against the depredations 
of predaceous and parasitic insects, the mother fills up 
the entrance with tiny pebbles. 
The Stone Osmia possesses the most highly developed 
instinct for the protection of the young against their 
parasitic enemies. This exceedingly interesting bee is 
one of the larger members of the family and builds in the 
larger branches of the pithed plants. A long burrow is 
chosen not under one-fourth inch in diameter. In the 
bottom of this she stores a mass of pollen and deposits 
her egg. She then builds an ample partition of chewed 
vegetable fibres closely resembling that of Alcidamea 
producta. Next she places a few little pebbles in the 
burrow and constructs another vegetable partition. About 
three cells are thus formed, the partitions being invariably 
composed of alternate layers of vegetable fibres and stones. 
When she has finished the partition for the last cell, 
the bee leaves an empty space about an inch long and 
fills it in with tiny pebbles from one-eighth to one-six- 
teenth of an inch in diameter. This stone-filled cell 
is then closed with five or six alternate layers of plant 
