To cite package ‘prism’ in publications use:

  Edmund M. Hart and Kendon Bell (2015) prism: Download data from the
  Oregon prism project. R package version 0.0.6
  https://github.com/ropensci/prism DOI: 10.5281/zenodo.33663

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {prism: Download data from the Oregon prism project},
    author = {Edmund M. Hart and Kendon Bell},
    year = {2015},
    note = {R package version 0.0.6},
    url = {https://github.com/ropensci/prism},
    doi = {10.5281/zenodo.33663},
  }