Bull. U. S. B. F., 1919-20. 



Pl.\te XVI. 



Fig. I. — Filaments of gill of fresh-w.i ; :: : .n : 1 ii.itural infcciinu of 



Plagiola donaciformis. Estimated lutul iminbcr ui yl^'-lii'-Iiii carried by fish 

 4,Soo. 



r 



i'<*' 



4.,, 



C^M; . 



Fig. 2. — Glochidia of washboard mussel, Quadnda heros. on 

 fin of fresh- water drum. Cyst very much enlarijed. 



. 3.— Section throujih vacated cysts on gill filaments; 

 Quadnda ebcnus vu river herring. 



