Printed Manilla Envelopes for Fish Scale Collection. 

Many scientists collect fish scales, make impression slides of the scales and store them in small envelopes along with the original scales for easy reference. Envelopes come with an un-gummed flap, and fit 1 x 3” slides. 
Printing includes: Scale sample #; species; length; weight; sex; state of organs; location; gear; date; collector.
Envelope dimensions: 57 x 89 mm (2.25 x 3.5”)

Please note that these are Manilla Envelopes, not "Rite in the Rain"