Pilsbry, H. A. 1946. Land Mollusca of North America (North of Mexico), Academy of Natural Sciences of Philadelphia. 2
      (2):1100-1102.

Pilsbry, H. A. 1945. Land Mollusca of North America (North of Mexico), Academy of Natural Sciences of Philadelphia.1
      (2):575-578, 875-885 

Steensma, K. M. M., Lilley, P. L., Zandberg, H. M. 2009. Life history and habitat requirements of the oregon forestsnail,
      allogona townsendiana (mollusca, gastropoda, pulmonata, polygyridae), in a british columbia population. Invertebrate
      Biology 128(3):232-242. 
      Link: http://onlinelibrary.wiley.com/doi/10.1111/j.1744-7410.2009.00168.x/abstract

Blinn, W.C. 1963. Ecology of the Land Snails Mesodon thyroidus and Allogona profunda. Ecology 44(3):498-505
      Link: http://www.jstor.org/sici?sici=00129658%281963%293%3C498%3AEOTLSM%3E2.0.CO%3B2-x&

Monroe J. E. 1967. The comparative histology and histochemistry of the digestive tract of the land snails
      Allogona townsendiana, Lea (herbivorus) and Haplotrema vancouverense, Lea (carnivorous). Thesis: Oregon State
      University 

Webb, G.R. 1948. Comparative observations on the mating of certain Triodopsinae. The 
      Nautilus 61:100-103.
      Link: http://www.biodiversitylibrary.org/page/8284802  

Hickman, C.P., L.S. Roberts, S.L. Keen, A. Larson and D.J. Eisenhour.  2009.
      Animal Diversity. McGraw-Hill, Boston, Massachusetts, USA

The Living World of Molluscs 2012.  <URL:
      http://www.molluscs.at/gastropoda/index.html?/gastropoda\morphology/tentacles.htm>. Accessed March
      29, 2012.

Encyclopedia of life. 2012.  <URL:
      http://eol.org/pages/579635/overview> Accessed 29, March 2012

Kingdom Animalia 2012. <URL:
      http://www.thefreedictionary.com/animal>. Accessed 29, March 2012