Key to the terrestrial gastropod genera of Wisconsin and nearby states
Adult Shells only!

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1a. Individuals without external shell
Slugs (not included in this key)
1b. Individuals with external shell
Go to 2
2a. Shell as wide or wider than tall
Go to 3
2b. Shell taller than wide
Go to 58
3a. Shell approximately as wide (.8-1.2x) as tall
Go to 4
3b. Shell obviously wider (>1.2x) than tall
Go to 8
4a. Shell umbilicate
4b. Shell imperforate to rimate
Go to 5
5a. Shell >10mm diameter
Go to 6
5b. Shell <10mm diameter
Go to 7
6a. Shell imperforate, peristome white, expanded
Neohelix group
6b. Shell narrowly umbilicate or rimate, peristome thin
7a. Peristome thickened, shell surface dull, suture absent, shell >3 mm diameter
7b. Peristome thin, shell surface satiny to glossy, suture deep, shell <3mm diameter
8a. Shell diameter >6mm
Go to 9
8b. Shell diameter <6mm
Go to 34
9a. Shell with open umbilicus
Go to 10
9b. Shell performate, imperforate or rimate
Go to 22
10a. Peristome expanded, usually white
Go to 11
10b. Peristome thin
Go to 15
11a. Shell diameter >16mm
Go to 12
11b. Shell diameter <16mm
Go to 13
12a. Parietal and peg-shaped basal lamella present
12b. Parietal lamella absent, basal lamella a low ridge
13a. Peristome continuous, 'y' or 'u' shaped on parietal surface
Polygyra group
13b. Peristome not continuous
Go to 14
14a. Basal and palatial lamellae present, umbilicus >2½ mm diameter
Triodopsis tridentata group
14b. Basal and palatial lamellae absent, umbilicus <2½ mm diameter
Stenotrema group
15a. Shell white, umbilicus >5mm wide
15b. Shell yellow to brown, umbilicus < 5mm wide
Go to 16
16a. Shell with spiral or transverse color markings
Go to 17
16b. Shell of single color
Go to 18
17a. Umbilicus, on average, <=1/5 shell diameter
17b. Umbilicus, on average, >1/5 shell diameter
18a. Shell >16mm diameter
18b. Shell <16mm diameter
Go to 19
19a. Umbilicus <1mm diameter
19b. Umbilicus >1mm diameter
Go to 20
20a. Umbilicus >1/3 shell diameter; shell surface dull, strongly ribbed
20b. Umbilicus <¼ shell diameter; shell surface shiny with indistinct ribs
Go to 21
21a. Shell diameter <7 mm
21b. Shell diameter >7 mm
22a. Peristome thin
Go to 23
22b. Peristome expanded, white
Go to 26
23a. Lamellae present on aperture base
Go to 24
23b. Lamellae absent within aperture
Go to 25
24a. Shell surface smooth
24b. Shell surface with thick, regularly-spaced ridges
25a. Whorl size increasing by at least 50% each revolution
25b. Whorl size increasing slowly in size, tighly coiled
26a. Shell rimate to umbilicate
Go to 27
26b. Shell imperforate
Go to 30
27a. Parietal lamella, if present, weak
Mesodon clausus group
27b. Strong parietal lamella present
Go to 28
28a. Basal and outer aperatural surface without lamellae, peristome not continuous above parietial lamellae
Stenotrema group
28b. Lamellae present on outer and basal aperatural surface
Go to 29
29a. Shell <10mm diameter, umbilicus <1mm diameter
Polygyra group
29b. Shell >10mm diameter, umbilicus >2mm diameter
Triodopsis tridentata group
30a. Palatal lamellae absent
Go to 31
30b. Palatal lamellae present
Go to 33
31a. Shell <13mm diameter, long parietal lamella extending most of aperture length
Stenotrema group
31b. Shell >15mm diameter, parietal lamella (if present) much shorter than aperture
Go to 32
32a. Shell at least twice as wide as tall
32b. Shell less than twice as wide as tall
Neohelix group
33a. Basal lamella a long ridge
33b. Basal lamella short, peg-like
34a. Shell imperforate
Go to 35
34b. Shell perforate to umbilicate
Go to 37
35a. Aperture wider than rest of shell, shell glassy, transparent
35b. Aperture less wide than rest of shell, shell transluscent to opaque
Go to 36
36a. Shell <2mm diameter
36b. Shell >2mm diameter
37a. Umbilicus <¼ diameter of shell
Go to 38
37b. Umbilicus >¼ diameter of shell
Go to 47
38a. Peristome expanded, white
Polygyra group
38b. Peristome thin
Go to 39
39a. Aperture strongly crescent-shaped, its width remaining approximately the same throughout
Go to 40
39b. Aperture oval, its width being much greater in the middle
Go to 41
40a. Top of shell with thick elevated ribs
40b. Top of shell with low, indented ribs
41a. Adult shells with 4-6 whorls which increase less than twice in width per revolution
Go to 42
41b. Adult shells with <4 whorls which increase twice or more in width per revolution
Go to 44
42a. Upper shell surface with dull luster and strong ribs
42b. Upper shell surface shiny and with weak ribs
Go to 43
43a. Last 1/5 of body whorl whitened from thickened shell; lamellae present in aperture
43b. Body whorl neither thickened nor whitened; lamellae absent
44a. Shell surface with regular, widely spaced, indented ribs
44b. Shell surface with irregular, closely spaced ribs
Go to 45
45a. Shell surface without faint spiral lines
45b. Shell surface with faint spiral lines
Go to 46
46a. Shell 2½-3½mm diameter; milky-white
46b. Shell 4½-5½mm diameter; rusty-brown
47a. Adult shell diameter >3mm
Go to 48
47b. Adult shell diameter <3mm
Go to 51
48a. Peristome white, expanded
Polygyra group
48b. Peristome thin
Go to 49
49a. Shell with prominent, raised spiral lines
49b. Shell without prominent, raised spiral lines
Go to 50
50a. Ribs small, approximately 10 per mm; shell color light yellow-brown
50b. Ribs large, approximately 5 per mm; shell color deep rusty-brown
51a. Peristome flared and usually thickened
51b. Peristome unflared and always unthickened
Go to 52
52a. Spiral lines present on protoconch
Go to 53
52b. Spiral lines not present on protoconch
Go to 54
53a. Whorl width increasing by at least 1.5x each revolution
53b. Whorl width increasing by less than 1.5x each revolution
54a. Ribs with distinct, sharp edges
Go to 57
54b. Ribs (if present) with indistinct, rounded edges
Go to 55
55a. Ribs not continuous, with regular pieces removed so that ribs look like a string of beads under high magnification; whorls increasing by at least 1.5 x per revolution
55b. Ribs continuous, whorls increasing by less than 1.5x per revolution
Go to 56
56a. Major ribs +/- 0.2mm tall, shell almost flat on top
56b. Major ribs (if any) <0.2mm tall, shell with clear dome
57a. Shell with domed spire; whorl base rounded; shell surface wrinkled
57b. Shell with flat spire; whorl base flattened; shell surface smooth
58a. Lax spiral with no more than 3 whorls in mature shell
Go to 59
58b. Tighter spiral with 4+ whorls in mature shell
Go to 61
59a. Aperture taking up ½ of shell
59b. Aperture taking up more than ½ of shell
Go to 60
60a. Shell and aperture broadly ovate
60b. Shell and aperture narrowly ovate to elongate
61a. Adult shell >4mm tall
Go to 62
61b. Adult shell <4mm tall
Go to 66
62a. Shell with glassy luster, transparent to transluscent, yellow to brown color
62b. Shell with silky to dull luster, opaque
Go to 63
63a. Peristome thickened or flared, white
Go to 64
63b. Peristome unthickened and unflared
Go to 65
64a. Lamellae present in aperture; shell white
64b. Lamellae absent in aperture; shell brown
65a. Shell <9mm tall, dark olive-brown color
65b. Shell >15mm tall, light gray-brown to white color
66a. Shell 1¼-1½ times taller than wide, with prominent 0.2mm elevated ribs
66b. Shell >1½ times taller than wide, ribs (if present) much less than 0.2mm tall
Go to 67
67a. Shell at least 2½ times taller than wide, shell white
67b. Shell 1½-2½ times taller than wide
Go to 68
68a. 0-2 lamellae present in aperture
Go to 69
68b. 3+ lamellae present in apreature
Go to 71
69a. Shell white
69b. Shell brown
Go to 70
70a. Shell >3mm tall
70b. Shell <3mm tall
71a. Shell brown, sinulus usually strong
71b. Shell white to clear, sinulus absent