AND EMBRYONIC FORMS. 453 



within, united more than half way down the posterior edges. Mantle rather thick, 

 very much thickened on the margin, colored on the posterior parts. Branchial open- 

 ing very large, with numerous small papillae, blackish inside and out. Anal opening 

 very large, blackish, mottled within. Super-anal opening small, edges black, united 

 for some distance below. Color of the mass whitish. 



Embryonic shell subtriangular, brown, has no hooks. Journ. Acad. Nat. Sci., (2,) 

 vol. iv. pi. 5, fig. 33, and Obs. vol. vi. p. 49. 



Columbus, Ohio, H. Moores. 



Remarks. — This species is closely allied to plana and decora, in the outward parts, 

 as well as the soft parts. It seems to differ more in its habits. In a letter from Mr. 

 Moores, he tells me that the specimens he sent me differ from plana, — the habits of 

 the species being peculiar to itself. That "it is found only in stony bottoms with 

 mud and sediment, and that it is more erect, more projecting out of the mud and 

 gaping wider when at rest than plana." 



Anodonta edentula = Alasmonta, Say. Disseminator, 1829. 



Branchial uterus occupies the whole length of the outer branchiae, having the ovi- 

 sacks placed transversely as described in unclulata. Branchice nearly semicircular, 

 very large, free almost half the length of the abdominal sack ; in the male the inner 

 ones are rather the larger. Palpi large, light-salmon color, transverse, subelliptical, 

 united one-third down the posterior edges. Mantle thin, thickened at the edges 

 where it is salmon color, and spotted black on the exterior up to the top of the anal 

 opening. Branchial opjening large, blackish-brown, with numerous rather small 

 papillae. Anal opening rather large, with minute, colored papillae along the whole 

 of the inner edge. Super-anal opening large, colored on the inner edges and macu- 

 late on the outer, united below. Color of the mass light-salmon, but darker on the 

 foot and the margin of the mantle. 



Embrycmic shell subtriangular, brown, has hooks. See Jour. Acad. Nat. Sci. (2) 

 vol. iv. pi. 5, fig. 37, and Obs. vol. vi. p. 50. 



Columbus, Ohio, H. Moores ; and Fox Eiver, Illinois, H. C. Grosvenor. 



BemarJcs. — This species has the same very remarkable transverse ovisacks as 

 undulata. (See ante.) It also has the super-anal opening fringed with minute pa- 

 pillae, but it differs in having the branchiae free. So that it cannot belong to either 

 of Prof. Agassiz's genera which he has made of the genus Anodonta. 



Anodonta Wahlamatensis, Lea. Trans. Am. Phil. Soe. (2), vol. vi. pi. 20, fig. 64. and Obs. vol. ii. p. 78. 



Branchial uterus occupies the whole length of the outer branchiae. Branchiae rather 

 large, nearly semicircular, inner ones much the larger, free nearly the whole length 

 of the abdominal sack. Palpi very wide and transverse, surrounding the mouth en- 



115 



