Also, in those bivalves with two adductor muscle scars of different sizes, the " posterior " scar will be the larger of the two and will be visible on both valves this condition is referred to as being " anisomyarian "; if the scars are of equal size, this is termed " isomyarian "; if the valve has only one muscle scar, this is termed " monomyarian ".
22.
""'Hemithecella " "'is a problematic genus of Ordovician mollusc proposed by Stinchcomb and Darrough in 1995 . " Hemithecella " belongs to what are informally known as multiplated molluscs; it is found in the late Cambrian of the Ozarks and the Lower Ordovician of the same region as well as in Minnesota and the southern Appalachian Mountains . " Hemithecella " has muscle scars identical to a monoplacophoran and not the musculature of a chiton to which some authors have suggested the multiplated molluscs belong.
