Transposition in a lamellibranch hinge, which describes the condition in which the right valve exhibits the hinge elements normally occurring in the left valve, and vice versa, is more common than sinistral vs. dextral coiling in gastropods. A left valve of Crassatella collina from the so-called Oligocene Sacate-Gaviota formation [California], showing hinge transposition, is described and figured. The writer proposes that such hinge transposition is an inheritable character.

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