EXPLANATION OF PLATE I. 
Unio Lutgo.us Lamarck, showing different parts of shell. 
Upper figure, right valve, exterior; middle figure, both valves 
viewed from above; lower figure, left valve, interior. A, Anterior 
end. P, Posterior end. D, Dorsal margin. V, Ventral margin. R, 
Right valve. L, Left valve. a, Anterior adductor muscle-scar (or 
cicatrix). b, Posterior adductor muscle-scar. c, Anterior foot . 
retractor muscle-scar. e, Posterior foot retractor muscle-scar. ct, 
Cardinal teeth. It, Lateral teeth. 1, Ligament. lg, Lines of 
growth. lu, Lunule. p!, Pallial line. u, Umbo. 
