Key to extant freshwater mussels of the Interior basin of North Carolina

How to use this dichotomous key...
"A dichotomous key consists of numbered, paired, statements of contrasting characteristics. In using a key, one reads the first couplet and decides which statement best describes the specimen at hand. Each statement indicates the number of the next couplet to be read. Couplet by couplet, the number of possible choices is reduced until the search terminates with the name of the taxon. If the specimen does not exactly match either statement, try both possible routes to an identification. It usually becomes evident that a wrong choice was made when the specimen clearly lacks the features mentioned in both statements of subsequent couplets." (Merritt and Cummins 1984).

Please Note: Red text is defined in the Glossary

a. poorly defined lateral teeth . . . . . . . . . . . . . . . . . . . . . . . . .2
b. well defined lateral teeth . . . . . . . . . . . . . . . . . . . . . . . . . . .6

a. pseudocardinal teeth vestigial or absent . . . . . . . . . . . . . . . 3
b. pseudocardinal teeth usually prominent . . . . . . . . . . . . . . . .4

a. lateral and pseudocardinal teeth completely lacking . . Pyganodon grandis giant floater
b. pseudocardinal teeth vestigial . . . . . . Strophitus undulatus creeper (formerly squawfoot)

a. pseudocardinal teeth tend to be lamellate, shells often more than 80 mm in length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Alasmidonta raveneliana Appalachian elktoe
b. pseudocardinal teeth triangular (chunky) . . . . . . . . . . . . . . . .5

a. shallow beak cavity; shell rarely more than 55 mm long . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Alasmidonta viridis slippershell mussel
b. deep beak cavity; shell rarely more than 35 mm long; periostracum often eroded . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pegias fabula little-wing pearlymussel

a. shell with nodules mostly on the posterior half of the shell surface . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Cyclonaias tuberculata purple wartyback
b. shell with no nodules on shell surface . . . . . . . . . . . . . . . . . 7

a. shell elongate, length to height ratio approximately 2 . . . . . . . . . . Elliptio dilatata spike
b. shell elliptical, truncate, or triangulate; length to height ratio less than 1.9 . . . 8

a. interdentum broad and thick, shells typically heavy and thick, particularly around the umbo .. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
b. interdentum narrow, shells thin to moderately thick . . . . . . . .12

a. shell light yellow with green rays . . . . . . ..Lampsilis fasciola wavy-rayed lampmussel
b. shell dull golden brown to dark brown or black, may have green rays . . .10

a. beak cavity deep . . . . . . . . . . . . . . . . . . . . . . . . . . . Fusconaia subrotunda longsolid
b. beak cavity shallow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

a. umbo just anterior to middle of dorsal margin . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Fusconaia barnesiana Tennessee pigtoe
b. umbo within the anterior third of the dorsal margin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Pleurobema oviforme Tennessee clubshell

a. well impressed anterior adductor muscle scar . . . . . . . . . . . . 13
b. anterior adductor muscle scar is shallow, not impressed; interdental projection usually present in left valve . . . . . . . . . . . . . . . . . . . . . . . . .Lasmigona subviridis green floater

a. periostracum yellow to greenish yellow, with green rays; nacre usually white to iridescent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..Villosa iris rainbow
b. periostracum tan or olive to dark brown or black with age, rays indistinct or absent; nacre usually purple . . . . . . . . . . . . . . . . . . . . . . . Villosa vanuxemensis mountain creekshell