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



Plate XMI. 



Fig. 2. — A >'(nmL: imi--^cl. Syviphynola 

 cosiaia, six days after completing the 

 stage of parasitism. ( Lef evre and 

 Curtis.) 



Fig. 1. — Glochidium oi Symphynota costata in process of transformation 

 during stage of parasitism. (Lcfcvre and Curtis.) 



Fig. %. — A yoimg squaw-foot mussel, Slrophiliis- cdtnlulits, which had 

 completed metamorphosis without parasitism; showing two adduc- 

 tor mussels, foot, gills, and rudiments of other organs of adult mussel. 

 (lyefevre and Curtis.) 



Fig. 4. — A young mucket. Lam/ysilis 

 liaamcntina, a week after the close of 

 the parasitic jjcriod. (Lele\Te and 

 Curtis.) 



