@misc{a._1905, 
  title={Clark on the Amount of Difference That Should Characterize Species and Subspecies The Limits of Difference in Specific and Subspecific Distinctions Hubert Lyman Clark}, 
  volume={22}, 
  DOI={10.2307/4070033}, 
  publisher={The American Ornithologists' Union}, 
  author={A.}, 
  year={1905}
  }