@misc{indiciae2b04c18f22ba,
  title = {Ordovician graptolites from the northern Sierra de Cobachi, Sonora, Mexico},
  author = {John F. Riva and Keith B. Ketner},
  year = {2011},
  doi = {10.1017/s0263593300014401},
  url = {https://pubs.usgs.gov/publication/70208973},
  note = {Source identifier: 70208973}
}