Plain pocketbook, Lampsilis cardium.  Click on the thumbnails for larger pictures. 
card004.jpg (24393 bytes) Gasconade River near Hartville, Missouri.  In Missouri, the inner sides of the mantle flaps are typically strongly marked with longitudinal stripes, reminiscent of the lateral stripes of Notropis shiners.
lcard1.jpg (16002 bytes) This picture and the one below are frame captures from VHS video and not of high quality.  However, they show the protruding, strongly pigmented, marsupial gills.  What appear to be pores along the margin are only indentations, and they are not (as commonly misconstrued) a route for glochidia release.  Glochidia are released when the gill is ruptured by the strike of a host fish. 
lcard5.jpg (15516 bytes) Notice that the end of one of the mantle flaps has been partly torn away- a common occurrence.  The marsupia are also torn by striking fish.  Presumably these tissues regenerate rapidly. 

Unio Gallery— Home Page http://unionid.missouristate.edu.  Copyright 1998-2006 by M. C. Barnhart.  Please see Usage Policy for conditions of use of images and video.