EXPLANATION OF PLATES. 

 Plate L 



1 — Unio falinlis; 2 — Unio jilans: 3 — I'nio siil)r()str;Un.s: 4— Uiiio riibi- 



ginosus; 5 — Mar.ii:irit;ui;i niariiiiiata: — t'liio liitcolns; 7 — AiKKloiita 

 ^ranclis: 8 — Aiiodonta tMleiituhis. 



Plate IL 



1, 2, 3, and 4 are pairs of L'. luteolus, wliieh exhibit gradations of form, 

 -color and size from the light straw-colored forms to the almost black 

 varietj'. 



a, b, c, d, e, f. g. and h exhibit the gradations of color and markings 

 found, from white to dark varieties, without I'egard to sex. 



