392 On the various Plumages of Butco sulitarius. 



B. borealis calwus, wliicli are dichromatic, as is also the 

 American Screech-Owl ; and in neither instance, so far as the 

 writer is aware, is there any cause to believe that the species 

 is changing into darker or lighter forms. 



Below are appended the measurements (in inches) of 

 twenty-seven specimens, from which Avill be apparent at a 

 glance, among other points, the constantly larger size of the 

 female : — 



Males. 



Female?. 



