AND EMBRYONIC FORMS. 449 



thick, oblique, subangular, united for a short distance down the posterior edges. 

 Mantle rather thin, with a very broad border, thickened on the edges anil having 

 small crenulations on the edges below the branchial opening. Branchial opening 

 very large, with very numerous small, brownish papillae. Anal opening small, with 

 numerous very small, brownish papillce. Super-anal opening very long, colored on 

 the edges and united for some distance below. Color of the mass dirty white. Ad- 

 ductor muscles enormously large and powerful. 



Embryonic shell subtriangular, brownish, has hooks. See Jour. Acad. Nat. Sci. (2), 

 vol. iv. pi. 5, fig. 29, and Obs. vol. vi. p. 49. 



Cincinnati, Ohio, J. Clark. 



Remarks. — This is our largest species of Margaritana and certainly one of the 

 most, if not the most, prolific of our Vhionidce. The females now under examina- 

 tion are not the largest in the exterior hard parts which I have seen, but their enor- 

 mous reproduction may be imagined by the facts stated above. In the four females 

 examined, the edges of the super-anal opening are united in two places, thus making 

 two openings above the anal opening; but the males had not this second attachment. 

 This may, however, vary in other specimens. 



Genus ANODONTA. 



Anodonta subcylindracea, Lea. Trans. Amer. Phil. Soc, vol. vi. pi. 24, fig. 117. Obs. vol. ii. 

 p. 106. 



Branchial uterus filled the whole length of the outer leaves, like fluviatilis. Bran- 

 chial large, slightly curved below, inner ones rather the larger, free nearly the whole 

 length of the abdominal sack. Palpi small, subtriangular, united on the posterior edges 

 nearly the whole length. Mantle very thin, with rather a narrow margin. Branchial 

 opening rather large, with closely set rows of papillae on the inner edges. Anal open- 

 ing rather small, with small papillae on the inner edges. Super-anal opening rather 

 small and united for some distance below. Color of the mass whitish. 



Embryonic shell belongs to the subtriangular group, and is nearly the same in out- 

 line as that of Margaritana rugosa, Bar. The specimens are from Buffalo, New York, 

 and kindly sent by Mr. A. T. Jackson. 



Anodonta imbecilis, Say. The Disseminator, 1829. 



Branchial uterus occupies the whole length of the abdominal sack. Branchial 

 large, slightly curved below, very nearly the same size, free nearly the whole length 

 of the abdominal sack. Palpi rather small, wide, triangular, not united at the pos- 

 terior edges. Mantle very thin, slightly thickened on the margin. Branchial open- 

 ing rather large, with numerous brown papilloa. The eye spots were perceptible on 



114 



