The following series of slides describe features of bivalves to illustrate and identify morphological characters and applicable terminology. I have emphasized distinguishing the right and left valves and the anterior and posterior sides; for, as Abbott said, "many identification features are used in relation to these orientations."  My plan is to add as I learn and photograph. There is no particular sequence.

 

When using this material to help identify your shells, keep in mind that not all families or genera are internally consistent and have the same features.  So, it can get difficult.  Use this material as a guide, but use it in conjunction with an authoritative source's description and use the two to firmly establish which valve you have and which side is anterior and posterior.  For example, within the Family Arcidae, Lunarca ovalis has beaks that point to the anterior side, but Noetia ponderosa has beaks that point to the posterior side.