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



Platk XIII. 



[See text, pace 139, and compare Plate XXI, fij,'. 1, 

 showing marsupiuni occupying: outer gills only. 

 Figures after Lclcvre and Curtis.] 



Fig. 1. — Niggerhead mussel, Quadrula cbcnu 

 marsupium. occupying all four gills. 



2. — Black sand-shell, Lampsilis recta; marsupium 

 occup>'ini; only posterior end of outer gills. 



Fig. 3. — Three-honied -warty-back, ObliQiiaria rejhxa; marsupium 

 occupying middle region of outer gills. 



Fig. 4. — Dromedary mussel, 

 Dromus dronias; marsupium 

 occupying only lower border 

 of outer gills. Anterior end of 

 «ill not included in marsu- 

 pium but uvcrhangi. it. 



Fig. 5.— Kidney _h 



 ■■-'. ■-.( , '.L. , ■.■■:(., lliai;,UJ.)UUll uCCUpyiUg CUtUC luWLT 



border uf outer gills aud much folded. 



