46 



Bryant Wai.ker 



Genus MEGALONAIAS Utterback, 1915. 



Shell large, heavy, obovate or rhomboid, alate post-dorsally, disk oblique- 

 ly folded; beaks sculptured with coarse, double-looped corrugations, which 

 extend over the upper surface of the disk as nodulous plications; epidermis 



dark-brown or blackish ; beak cavities narrow and deep ; anterior muscle 

 scars deep and filled with a nacreous deposit, posterior scars large and in- 

 distinct. 



Fig. 149* 



Type: Unio heros Say, fig. 148. Animal, fig. 149. 



* The following lettering applies to figs. 149, 165 and 201 : 

 A. — Anal opening. F. — Foot. P. — Palp. 



Av. — Antero-ventral margin. I. — Inner gill. S. — Supra-anal opening. 



B. — Branchial opening. M. — Marsupium. 



