422 UNIONIDiE, THEIR SOFT PARTS 



down the posterior edges. Mantle thin, thickened at the edges. Branchial opening 

 small, with a few brownish papillse. Anal opening rather large, with numerous 

 small, brownish papillae. Super-anal opening rather small, united below. Color of 

 the mass whitish. 



Flint River, Butler County, Georgia, H. M. Neisler, M. D. 



Remarks. — A single specimen only was received in alcohol. Although the habitat 

 is so far removed from specimens sent by Dr. Emmons from N. Carolina, I cannot 

 perceive any difference in the characters of the outward hard parts. 



Unio monodontus, Say = soleniformis, Lea. Disseminator, 1829 ; and Am. Conch., pi. 6. 



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

 rium. Branchiae very wide and short, nearly straight below, the inner ones much 

 the larger, free two-thirds the length of the abdominal sack, the posterior extremity 

 not attached to the mantle as it usually is, but is unconnected for nearly half an 

 inch, the point standing out free and some distance from the edge of the mantle. 

 Palpi very large, transverse, subfalcate, united more than half way down the pos- 

 terior edges. Branchial opening brownish, very large, with numerous irregular 

 papillae in groups. Anal opening large, black on the inner edges, with very small 

 papillae. Super-anal opening rather larger, black on the inner edges, not united 

 below. Color of the mass dirty white. The abdomen is long and rather lank, the 

 foot being at the anterior end and not along the whole inferior part of the abdomi- 

 nal sack as usual. 



Ohio River at Jeffersonville, Indiana, Capt. S. S. Lyon, U. S. Engineer Corps. 



Remarks. — It is to be regretted that none of the specimens had the embryos 

 matured enough to observe the form of the embryonic shell. The form of the 

 outer hard parts as well as the soft parts is so different from other Unionidce, except 

 Margaritana margaritifera, that we might expect to find a strong variation in the 

 important part of the embryonic shell, but, unfortunately, we have not yet seen 

 the embryonic shell of either of them. The most remarkable characteristic of both 

 these shells is the off-setting posterior point of the branchiae. I have not seen it in 

 any other of the numerous species which I have examined. In other characters 

 there are also strong affinities. See description of M. margaritifera, Journal Acad. 

 Nat. Sci., (2,) vol. iv. p. 224 and Obs. vol. vii. p. 42. In one of the specimens exa- 

 mined I found the two inner leaves of the branchiae united in a line from top to 

 bottom. 



Unio pattjlus, Lea. Trans. Amer. Phil. Soc, (2,) vol. iii. pi. 12, fig. 20. Obs. vol. i. p. 55. 



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



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



