KEY TO THE ENTOMOSTRACA OF COLORADO 269 



cent alcohol is commonly recommended, my practice has been to use 

 formalin, adding a few drops to the water when the collection is 

 bottled. Small vials are convenient for storing material. Collec- 

 tions should be carefully labeled at the time they are made. 



For the study of many parts used in the identification of species 

 it is necessary to make dissections. On account of their small size, 

 most specimens must be dissected with needles under a lens or a 

 binocular dissecting microscope. This is best done on a sHde in a 

 drop of glycerin. For the study of these forms, a compound micro- 

 scope is, of course, necessary. For permanent mounting of specimens, 

 glycerin may be used, but unless the cover is well sealed the prepara- 

 tion will not last long. I have used glycerin jelly with good results. 

 This medium has the disadvantage that it requires to be heated when 

 used, and the compensating advantage that it becomes soHd when 

 cool, giving a more durable mount. The cover should, however, be 

 cemented. Specimens may also be dehydrated, cleared, and mounted 

 in balsam, but in this process cuticular structures are likely to be 

 deformed, and some preparations also become too transparent. 



The figures used in the following key were either drawn from 

 nature or redrawn from the sources indicated in the legend. Mr. 

 George T. Kline made Figs. i-6, 9, 10, 12-18, 20, 26, 32, 34, 36-41, 

 45, 47, 54, 60, 61. For opportunity to make the collections, I am 

 indebted to Professor Francis Ramaley of the University of Colorado, 

 who placed at my service facilities provided for the summer field 

 work of the University. During the course of the work, valuable 

 suggestions were received from Professors Chancey Juday and A. S. 

 Pearse of the University of Wisconsin. Of great service to me were 

 proofs of certain chapters of Ward and Whipple's Fresh-Water Biology, 

 which I secured through the courtesy of the publishers, John Wiley 

 & Sons. 



