50 BROOKLYN MUSEUM SCIENCE BULLETIN 3. 3. 
The head is generally less variable. The sculpture varies a little. 
The impressed median line is generally distinct and varies slightly. The 
antennal joints, especially the second, third and fourth, are variable in 
length in specimens of the same species. 
The sexual differences are very pronounced in some species, in 
others feebly so. The males generally are smaller and narrower than 
the females, the eyes more prominent, antennal joints more elongate, 
the intercoxal process of the mesosternum often narrower and the first 
abdominal segment usually shorter than in the female. The form and 
armature of the posterior femora is entirely different in the two sexes of 
some species, in others differs scarcely from those of the females but the 
form is generally a little more robust and longer in the males. The 
first ventral segment is occasionally broadly depressed at middle in the 
male, rarely in the species of the subgenus Donacia, but nearly always 
more or less distinctly in the species of the subgenus Plateimiaris. The 
last ventral and dorsal segments are generally truncate at. apex in the 
male and the last dorsal segment of some species emarginate in both 
sexes, in others only in the male. The last ventral and dorsal segments 
of the females are generally more or less distinctly triangularly converging 
to apex and either narrowly or broadly rounded at apex, occasionally 
they are quite elongate. In those species of which the males and females 
are nearly alike the sex of the specimen at hand is often difficult to 
determine, however, the males of all the species have at middle of the 
last ventral segment at apex a more or less deep depression. 
Donacias in the adult stage generally feed on the pollen of flowers 
of aquatic, semiaquatic and palustral plants including reeds, sedges, etc., 
and each species is possibly partial to a certain plant in which they 
probably also breed. However, some species will feed on the pollen of 
flowers of a variety of plants but undoubtedly only in the absence of 
their natural or preferred food plant. Specimens of suhtilis collected by 
Mr. W. E. Snyder at Beaver Dam, Wisconsin, were labelled "on Golden- 
rod blossoms." Mr. C. A. Frost found in Maine a number of specimens 
of emarginata and a few of metallica on the flowers of the spiked maple, 
also specimens of sulcicolUs in copula in the flowers of Primus. Mr. 
Davis and myself took specimens of liehecki on the flowers of the white 
daisy, a Donacia which is generally found on the flowers and leaves of 
the white water lily. This latter case, however, is explained by the 
adjacent lake being dredged there were scarcely any water lilies left to 
feed upon. Mr. Wenzel found liehecki in numbers on the flowers of 
three different aquatic plants. The time of appearance and greatest 
