AND EMBRYONIC FORMS. 431 



below, inner ones very much the larger, united the whole length of the abdominal 

 sack. Palpi large, thick, rather oblique, suboval. Mantle thin, double along the 

 inferior edges. Branchial opening very large, with small, dark papilla. Anal open- 

 ^rather large, with numerous, very small, brownish papilla. Super-ana! opening 

 rather large, slightly colored on the edges and united below. Color of the mass 

 whitish inclining to salmon. 



Embryonic shell almost exactly the same with multiracliatus. See Jour. Acad Nat 

 Sci. (2), vol. iv. pi. 5, fig. 17, and Obs. vol. vi. p. 47. 

 Cincinnati, Ohio, J. Clark. 



Unio plicatus, Lesueur, Say. Nich. Ency. Am. Ed. Art. Conch. 



Branchial uterus _. No ova were found here, but they were in the ovarium 

 Branches large, rather thick, rounded below, inner ones much the larger, free two- 

 thirds the length of the abdominal sack. Palpi rather small, subelliptical, rounded 

 at the end, united one-third down the posterior edges. Mantle rather thin with a 

 very broad border. Branchial opening very large, with numerous small papilla, 

 Anal opening rather large, with very minute papilla. Super-anal opening remarkably 

 large, colored on the edges and slightly united below. Color of the mass whitish 

 • Cincinnati, Ohio, J. Clark. 



Unio lacrymosus, Lea. Trans. Am. Phil. Soc. (2), vol. iii. pi. 6, fig. 8, and Obs. vol. i. p. 14. 



Both specimens received were males. Branchice very large, inner ones very much 

 the larger, rather thick, very much rounded below, free nearly the whole length of 

 the abdominal sack. Palpi very large, transverse, rather thin, subelliptical, united 

 half way down the posterior edges. Mantle rather thin, with a broad and thickened 

 margin. Branchial opening very large, with numerous rather small branched papilla 

 Anal opening rather small loitlwut papilla,. Swper-anal opening very large slightly 

 colored on the edges, united for a small distance below. Color of the mass whitish 



Cincinnati, Ohio, J. Clark and D. H. Shaffer. 



Memarks.-Some of these specimens were in a living state, as well as in alcohol. I 

 could not find any papillae in the anal opening of any of them. 



Unio securis, Lea. Trans. Amer. Phil. Soc., (2), vol. iii. pi. 11, fig . i 7 . bs. vol. i. p. 51. 



Branchial uterus occupies the posterior half of the outer branchiae, blackish on the 

 inferior margin, with about twenty ovisacks on each side, very like to cariosus 

 Branchial rather large, very much rounded below, inner ones the larger, free nearly 

 half the length of the abdominal sack. Palpi small, subtriangular, united a short 

 distance down the posterior edges. Mantle very thin, dark along the edges, with a 

 wide margin, slightly thickened and fringed below the branchial opening. Branchial 



