220 SEVENTEENTH Report STATE ENTOMOLOGIST oF MINNESOTA—1918 
TRY POXYLONIDAE 
Head not wider than the thorax; eyes always deeply emarginate within, or reni- 
form; front wings with two submarginal cells, the second more or less indistinct; 
middle tibia with only one apical spur; abdomen elongate, clavate, first segment 
elongate, petioliform; a strong constriction between the first and second abdominal 
segments. 
These are slender wasps without 
yellow bands on abdomen. . They 
make cells in pithy plants, separating 
them by mud partitions, or they make 
mud cells against walls near or in 
houses. These nests are stored with 
spiders. Some of them, Tryposylon 
albitarse, for example, according to 
Walsh, select the deserted cells of a 
mud dauber, provisioning its nest with 
spiders. Another species, 7. carini- 
frons, stores its cell with aphids. We 
figure a female of Trypoxylon biden- 
tatum Fox, from a Minnesota speci- 
Fig. 109. Trypoxylon bidentatwm Fox, 
female. men. 
MELLINIDAE 
Mesosternal suture wanting; intermediate coxae contiguous; middle tibia with 
two apical spurs; abdomen with a more or less distinet constriction between the first 
and second segments, first segment coarctate. 
There is only one genus of this family, containing three species, 
in America. There are therefore scanty if any observations on the 
group in this country. Members of the genus Mellinus have been ob- 
served on patches of cow dung feigning death, only to grasp a blue bot- 
tle fly which came within reach. 
The European species M. arvensis provisions its nest with small 
Diptera, including Stomo.xys calcitrans, the stable fly. 
SPHECIDAE 
Antennae inserted above the base of the clypeus. Mesosternum not produced into 
an elongate process; prothorax usually transverse; femora normally not swollen in 
the middle; prepectus present; abdomen distinctly petiolate, no constriction between 
first and second segments. 
Comstock calls these ‘“‘thread-waisted” wasps because the most 
striking characteristic is the fact that the first segment of the abdomen 
forms a long, smooth, round petiole suggesting the name. Unlike the 
