Diplocardia is a genus of North American (USA, Mexico) earthworms with 52-57 known species that is remarkably similar to Australian Diplotrema Spencer, 1900.
Blakemore, R.J. (2005). American earthworms from north of the Rio Grande - a species checklist. COE, YNU. Retrieved on 10 May 2005 [1][permanent dead link]
Blakemore, R.J. (2006). American earthworms from north of the Rio Grande - a species checklist (2nd edition). COE, YNU. Retrieved on 13th Dec, 2006 [2]
James, S.W. (1995). Systematics, biogeography and ecology of earthworms from eastern, central, southern and southwestern USA. in P. Hendrix (ed.) Earthworm Ecology and Biogeography in North America, pp. 29–51. CRC Press, Inc, Boca Raton, Florida. Retrieved on 4th Mar, 2008 from Google Books