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Ancotrema voyanum (Newcomb, 1865)
Key Characteristics: Diameter 11-15 mm. Shell translucent to opaque, with 5-5.5 whorls. Spire flat or barely elevated, suture moderately impressed, crenulated. Whorls smooth at first, developing closely-set, round-topped, collabral ribs on second whorl. Ribs extending from suture to umbilicus, their tops cut by incised spiral striae. Body whorl rather closely coiled, not markedly descending. Aperture oblique, semicircular to triangular in basal view. Lip weakly turned outward, with narrow, crustose border. Upper limb of peristome produced, markedly downturned, sinuous. Parietal callus with raised rim. Shell white under gray or grayish yellow, dull periostracum; peristome sometimes orange-brown.
Ancotrema voyanum has a higher spire, narrower umbilicus and coarser collabral ribbing than Ancotrema zopherum Roth, 1990, and the ribbing becomes prominent earlier on the spire. Haplotrema alameda Pilsbry, 1930, differs in having narrow, lamellar ribs that are not cut by spiral striae. Haplotrema mokelumnense Roth, 1990, has only low rugae, not collabral ribs.
Key to the Species of Ancotrema in California
| 1 | Beaded shell sculpture (round-topped radial ribs cut by spiral striae) present over entire shell including body whorl | 2 |
| Beaded sculpture confined to spire; body whorl smooth or with low, radial wrinkles | A. hybridum (Ancey, 1888) | |
| 2 | Shell moderately to strongly depressed (height/diameter ratio usually greater than 0.45; ribbing strong from outset | 3 |
| Shell very strongly depressed (height/diameter ratio 0.34 to 0.43); ribbing weak before third neanic whorl | A. zopherum Roth, 1990 | |
| 3 | Shell 13-22 mm in diameter; base of spermathecal duct strongly dilated; penial retractor muscle originating on left side of columellar muscle; vagina very short | A. sportella (Gould, 1846) |
| Shell 11-15 mm in diameter; base of spermathecal duct weakly dilated; penial retractor muscle originating on floor of lung with strands from columellar bundle; vagina almost equal to length of penis | A. voyanum |
Synonyms: Haplotrema voyanum (Newcomb); (?) H. v. humboldtense Pilsbry, 1946; Selenites voyana var. simplicilabris Ancey, 1882
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