The Systematic Position of Helminthoglypta traskii fieldi Pilsbry, 1930 (Gastropoda: Stylommatophora)
Dissection of the genitalia of the snail described as Helminthoglypta traskii fieldi shows that it belongs to the so-called Helminthoglypta ayresiana series, a small group of species of coastal, south-central California and the northern Channel Islands. Comparison with other members of the group suggests recognition of it as a distinct species, H. fieldi. Pleistocene and post-glacial climatic conditions appear to have influenced distribution of the group.
"The Systematic Position of Helminthoglypta traskii fieldi Pilsbry, 1930 (Gastropoda: Stylommatophora),"
Bulletin of the Southern California Academy of Sciences:
Available at: http://scholar.oxy.edu/scas/vol72/iss3/4