http://strata.ummp.lsa.umich.edu/jack/showgenera.php?taxon=611&rank=class
916
https://archive.org/stream/bulletinsofameri363pale#page/n3/mode/2up
6
http://citation.dbpedia.org/hash2/157db80e8301580dcdf0809a9f434d2838298ac66dae8f723ddfb110a012aa5e
5
http://strata.ummp.lsa.umich.edu/jack/showgenera.php?taxon=575&rank=class
2
http://strata.ummp.lsa.umich.edu/jack/showgenera.php?taxon=279&rank=phylum
1
http://books.google.com/books?vid=ISBN9780877104506100877104506
1
http://books.google.com/books?vid=ISBN9780877104506
1
http://biodiversitylibrary.org/page/10698872
1
https://archive.org/stream/bulletinsofameri363pale/bulletinsofameri363pale_djvu.txt
1