. The Canadian field-naturalist. November, 1934] The Canadian Field-Naturalist 135 A NEW SPECIES OF GYRAULUS FROM CANADA By FRANK C. BAKER Curator, Museum of Natural History, University of Illinois, Gyraulus hornensis nov. sp. Gyraulus arcticm Baker, Fresh Water Mollusca of Wisconsin, Vol. 1, p. 381, plate xxii, Fig. 34-37, 1928, Bui. 70. Wis. Geol. Nat Hist. Surv.; Baker and Cahn, Freshwater Mollusca from Central Ontario, Annual Report, National Museum of Canada, 1929 p 59, 1931 (part). Not Planorbis arcticus (Beck MS) Moller, Index Moll. Greenland, p. 5, 1842. Shell depressed, the periphery
. The Canadian field-naturalist. November, 1934] The Canadian Field-Naturalist 135 A NEW SPECIES OF GYRAULUS FROM CANADA By FRANK C. BAKER Curator, Museum of Natural History, University of Illinois, Gyraulus hornensis nov. sp. Gyraulus arcticm Baker, Fresh Water Mollusca of Wisconsin, Vol. 1, p. 381, plate xxii, Fig. 34-37, 1928, Bui. 70. Wis. Geol. Nat Hist. Surv.; Baker and Cahn, Freshwater Mollusca from Central Ontario, Annual Report, National Museum of Canada, 1929 p 59, 1931 (part). Not Planorbis arcticus (Beck MS) Moller, Index Moll. Greenland, p. 5, 1842. Shell depressed, the periphery rounded; colour light corneous, surface shining; sculpture of fine, oblique lines of growth with very fine spiral lines, more or less conspicuous; nuclear whorls small, rounded, spirally striate in sculpture; whorls about four, rapidly enlarging, the last somewhat expanded near the aperture, round- ly angled at the periphery of the last whorl, the upper part of the body whorl slightly flattened; spire flat, the whorls coiled in the same plane; the body whorl may be nearly in line with the spiral turns or it may be deflected about a third of the distance from the aperture; sutures deeply channelled; base concave exhibiting all of the whorls, the um- bilical region wide, but the body whorl well rounded, not flattened or having a reamed- out appearance; aperture obliquely, ovately rounded; lip thin, sharp, simple, or slightly thickened with a callus deposit; parietal wall with a white callus. Height Gr. Diameter Aperture heieht Diameter in mm. ] .5 Holotype Para type Paratyoe The last specimen with deflected body whorl. Type Locality: Birch Lake, Horn River, about 75 miles above the Mackenzie River, Mackenzie District, Canada. Collected by Mr. E. J. Whittaker, July, 1921. Types: Museum of Natural History, Univer- sity of Illinois, No. Z13072a. This small planorbid was erroneously refer- ed to arcticus in the Fresh Water Mollusca of Wisco
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