INTRODUCTION 39 
tures can then be seen only with difficulty. After being cleared, 
the genitalia should be washed for 10 minutes in water. Com- 
plete dissection is accomplished under glycerine in a watch glass 
under a high power of the binocular microscope. 
Several methods of storing such dissections have been used. 
The one preferred involves small glass vials, glycerine, and small 
corks. The glycerine is placed in the bottom of the vial, the 
dissected specimen is immersed in the glycerine, and the cork 
(the tip of which is covered with balsam) seals the preparation. 
Balsam and glycerine apparently do not mix and vials corked 
in this way for a number of years have remained in excellent con- 
dition. The vial is subsequently placed on the pin with the speci- 
men; thus the adult, the labels, and the vial enclosing the geni- 
talia may be kept together on a single pin in the collection. 
Various other methods of preparation have been used, such 
as slide or point mountings, but such mounts either discolor, are 
partly obscured, or must be stored separately. 
SYNONYMY 
Much of the synonymy given is that proposed by the late J. M. 
Aldrich, who examined type specimens of many North American 
species in European museums. In some instances his new 
synonymy was left only in note form. Synonymy in the Luciliini 
is that given by Aubertin in 1933. 
I have studied most of the types of North American ealli- 
phorid flies in North American museums but have examined only 
a few which are in European museums. The keys to the Chryso- 
myini were sent to all European museums in which type speci- 
mens of North American species are deposited and these type 
specimens were run through the keys by competent dipterists. In 
some respects this course was not entirely satisfactory, but it was 
the only way in which the identity of many of the old types 
eould be determined. ‘ 
A considerable part of the synonymy given by Bezzi in the 
1907 Palaearetie Catalog of Diptera is not repeated for species 
supposedly occurring in both North America and in the Palae- 
arctic Region. In many points this work has been found to be 
erroneous and only type examination will clarify such synonymy. 
CLASSIFICATION 
The purpose of the key to larger groups in this work is to de- 
fine the family Calliphoridae. No attempt is made to show ac- 
tual affinities of calypterate or acalypterate flies other than 
those of the calliphorid stem. 
