AND EMBRYONIC FORMS. 451 



found fifteen more ; 16th, there were forty-six additional ; 17th, only three were found ; 

 18th, only two ; from the 18th to the 21st, fifteen • on the 22d and 23d eight more, 

 four of them were in the act of passing out between the valves of the parent. They 

 all had the young shell attached to the outside of the ovisack, with the valves open. 

 One of them stood out distinctly, attached by a transparent filament nearly its own 

 length. From the 23d to the 30th, over a hundred ovisacks were extruded ; 31st, sixty 

 ovisacks appeared, the young all looking healthy, but I could not observe the least 

 motion in any of them, nor have I in any of this species. February 2d, ninety 

 made their appearance ; Feb. 3d, over ninety ; on the 4th and 5th, about two hundred 

 and sixty ; on the 5th, one hundred and seventy ; on the 6th and 7th, one hundred 

 and four; from the 8th to the 13th, only thirty-five, and subsequently none were 

 extruded. Anodonta edentula has also this singular construction of branchial uterus, 

 and these two species are the only ones I have known to present this remarkable 

 structure. 



Anodonta Perussaciana, Lea. Trans. Amer. Phil. Soc. (2), vol. v. pi. 6, fig. 16. Obs. vol. i. p. 157. 



Branchial uterus occupies apparently the outer leaves of the branchiae, which are 

 brownish. One specimen had half the anterior portion filled ; evidently, the pos- 

 terior portion had been discharged. Branchial large, the inner ones rather the larger, 

 free nearly half the length of the abdominal sack. Palpi very large, semilunar, 

 rather thin, united only a small distance down the posterior edges. Mantle rather 

 thick, double along the lower edge, which has papilla? below the branchial opening. 

 Branchial opening large, with numerous small, brownish papilla?. Anal opening 

 small, with numerous very small papilla?.* Super-anal opening rather long, colored 

 on the outer edges with black pigment and united for some distance below. Color 

 of the mass light salmon. 



Embryonic shell triangular, brown, no apparent hooks in the specimens examined. 

 See Journ. Acad. Nat. Sci., (2), vol. iv. pi. 5, fig. 35. Obs. vol. vi. p. 50. 



Scioto River, near Columbus, Ohio, H. Moores. Common in the Ohio basin. 



Anodonta Couperiana, Lea. Trans. Am. Phil. Soc. (2), vol. viii. pi. 20, fig. 46. Obs. vol. iii. p. 65. 

 Branchial uterus occupies the whole of the outer branchiae, like fluviatilis, giving 

 a reddish appearance to the whole leaf and extending slightly below the inferior 

 edge. Branchial large, nearly semicircular, inner one rather the larger, free rather 

 more than the half of the length of the abdominal sack. Palpi rather small, sub- 

 triangular, united for a short distance down the posterior edges. Mantle thin, thick- 



* This species has perfectly formed papilla; on the edges of the anal opening, and therefore cannot belong to 

 the genus Anodonta as described by Agassiz, who says, " anal opening not fringed." It is nevertheless a true 

 Anodonta according to, I believe, all other authors. 



