Allogona townsendiana

Allogona (Dysmedoma) townsendiana (I. Lea, 1838)
Oregon Forestsnail

  • Helix townsendiana I. Lea 1838: 99, pl. 23, fig. 80.
  • ? Helix (Nanina) ruida Gould 1846 (1846–1850): 178.
  • Polygyra townsendiana var. brunnea Vanatta 1924: 25.
  • Allogona (Dysmedoma) townsendiana f. frustrationis Pilsbry 1940: 885, figs 509f , 510(1, 1a, 3).
Allogona townsendiana; NE of Hood Canal Bridge, Jefferson Co., Washington (RGF 1636); width 25.7 mm.

Identification. Shell depressed-heliciform. Spire conical. Whorls ca 6, rounded. Last whorl descending at aperture. Suture moderately impressed. Periphery rounded. Teleoconch with wide, not quite evenly spaces, low, axial riblets, coarser and less even than in P. ptychophora; spaces granular between striae (below suture and in the umbilical region), with closely spaced, spiral striae. Aperture subovate, edentulous, nearly as high as wide. Palatal and basal lips thickened, expanded, slightly recurved, contracted behind. Umbilicus open, overhung by columellar lip. Periostracum without hairs. Shell pale light brown or yellowish, eroding greyish, with pale, straw-yellow streaks. Width to 26–33 mm (wider than high).

This species is most similar to Allogona ptychophora but differs in being larger and has coarser, more irregular axial riblets below the sutures and is frequently sculptured with fairly strong malleations.

Animal greyish brown; tentacles and spaces between tubercles darker.

Allogona townsendiana
Allogona townsendiana; Kent Municipal Cemetery, on the slope of Cemetery Hill, near Agassiz, BC, May 2013.

Habitat. In moist forests, generally. Often especially common in patches of stinging nettle.

Global range. BC south through coastal Washington to north-western Oregon (Pilsbry 1940).

Canadian range. South-western British Columbia: Hope and west in the Fraser river valley to Burnaby; Westholme, north of Duncan on Vancouver Island.

The record of Polygyra ptychophora from “Mission Junction,” cited Whiteaves (1906) almost certainly refers instead to this species.

Etymology. Named after John K. Townsend (1809–1851), ornithologist and naturalist from Philadelphia, who accompanied Thomas Nuttall on the 1834–35 Wyeth Expedition across the Rockies to Fort Vancouver on the Columbia River west to Oregon, collecting biological samples (Moring 2002).

Remarks. Pilsbry (1940) recognized two “forms” (not subspecies): brunnea Vanatta, 1924, and frustrationis Pilsbry, 1940. The brunnea form is characterized by having a darker shell, which occurs with normally pigmented shells in some populations throughout the range of the species, and it is almost certainly nothing other than a colour variant. Likely an ecophenotype, frustrationis was proposed for a form from Cape Disappointment, Washington, which was said to have relatively thinner and smoother shelled (Pilsbry 1940). Recently, Burke (2013) recognized this taxon as a putative subspecies, Allogona townsendiana frustrationis, although his reasons for this separation seem weak, and no subspecies are considered here.

  • Burke TE (2013) Land snails and slugs of the Pacific Northwest. Oregon State University Press, Corvallis, Oregon, 344 pp.
  • Gould AA (1846–1850) [Shells collected by the United States Exploring Expedition under the command of Charles Wilkes.] Proceedings of the Boston Society of Natural History 2: 141–145, 148–152 [July 1846]; 153–156, 159–162, 165–167 [August 1846]; 170–173, 175–176 [September 1846]; 177–179, 180–184, 185–187, 190–192 [“November 1846”; probably between 16 December 1846 and March 1847]; 196–198, 200–203, 204–208 [March 1847]; 209, 210–212, 214–215, 222–224 [June 1847]; 225, 237–239 [July 1847]; 251–252 [December 1847] • 3: 73–75 [November 1848]; 83–85, 89–92 [March 1849]; 106–109 [April 1849]; 118–121, 140–144 [May 1849]; 151–156, 169–172 [January 1850]; 214–219 [May 1850]; 252–256 [June 1850], 276–278 [July 1850]; 292–296, 309–312 [November 1850]; 343–348 [December 1850].
  • Lea I (1838) Description of new freshwater and land shells. Transactions of the American Philosophical Society (New Series) 6: 1–154.
  • Moring J (2005) Early American naturalists: exploring the American West, 1804–1900. Taylor Trade Publishing, Lanham, MD, 241 pp.
  • Pilsbry HA (1940) Land Mollusca of North America (north of Mexico). Vol. I, Part 2. The Academy of Natural Sciences of Philadelphia, Monographs3: i–viii + 575–994 + i–ix.
  • Vanatta EG (1924) Descriptions of four new American shells. Proceedings of The Academy of Natural Sciences of Philadelphia 76: 25–27.
  • Whiteaves JF (1906) Notes on some land and fresh water shells from British Columbia. The Ottawa Naturalist 20: 115–119.