AND EMBRYONIC FORMS. 447 



Margaritana arcula, Lea. Trans. Arner. Phil. Soc, vol. vi. pi. 22, fig. 69. Obs. vol. ii. p. 71. 



Branchial uterus probably occupying botb the outer branchiae.* The ova in the 

 ovarium were not mature. Branchial very large, almost semicircular, inner ones 

 much the larger. The specimen with ova had the branchiae united the whole length 

 of the abdominal sack. The other (probably a male) has a small opening into the 

 cavity above at the posterior part of the abdominal sack, which I thought at first 

 might be accidentally torn in opening, but, on close examination, it does not appear 

 to be the case. It would be singular if the female should be closed and the male 

 free. Palpi rather small, subtriangular, united half way down the posterior edges. 

 Mantle moderately thick and double at the margin. On the outer edge, more than 

 half way round the posterior outer edge, maculate with beautiful dark-brown, 

 quadrate spots. Branchial opening rather small, with reddish-brown, rather small, 

 low, conical papillae. Anal opening rather small, with very small papillae along the 

 inner edges, which edges are irregularly colored. Super-anal opening rather small, 

 united below for a distance about equal to the opening. All this outer edge is beau- 

 tifully maculate with dark-brown, quadrate spots. Color of the mass white. The 

 large cavity of the beaks seems to be filled up by a puffy enlargement of the 

 mantle. 



Altamaha Eiver, near Darien, Georgia, J. Hamilton Couper, Esq. 



Margaritana Hildrethiana, Lea. Trans. Amer. Phil. Soc., vol. v. pi. 3, fig. 8 and Obs., vol. i. p. 148. 



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

 large, inner one slightly larger anteriorly, curved below, free about half the length 

 of the abdominal sack. Palpi small, very thin, suboval, slightly united on the upper 

 posterior edges. Mantle thin. Branchial opening large, with numerous rather small 

 papillae. Anal opening large, apparently without papillae. Super-anal opening large, 

 united below. Color of the mass whitish. 



Embryonic shell subrotund, clear white, has no hooks. See Journ. Acad. Nat. Sci., 

 vol. iv. pi. 5, fig. 31, and Obs. vol. vi. p. 49. 



Columbus, Ohio, H. Moores. 



Remarks. — This, like rugosa and marginata, seems to have no papillae on the edges 

 of the anal opening, while arcula has. If the absence of papillae on the anal 

 opening should characterize the genera Anodonta, Margaritana, Alasmodonta and 

 Strophitus, as amended by Prof. Agassiz, some of these Margaritanai would have to 

 be placed in another group. 



Two specimens only were received, In one there were .1 lew oxn in Lhe outer branchiae. These branchiae, 

 in both specimens, had acrimpled appearance, which may have been caused by the aleohc4; but this is nut the 

 case with the inner branchiae, which are perfectly smooth. Therefore the crimpling may be natural. 



