Bull. U. S. B. F. (No. 1103.) 
Figure 18. — Specimens of buckhorn, Tritogonia verrucosa (Rafinesque) (on left), Mississippi River, Fairport, Iowa; and Pope’s 
purple, Unio popei Lea (on right), Rio Grande Valley near Mercedes. Tex. Upper buckhorn, 10.22 centimeters; lower 
buckhorn, 7. Go centimeters; upper purple, 9.2G centimeters; lower purple, 8.3G centimeters in length 
