AND EMBRYONIC FORMS. 441 



papillm or crenulathns. Super-anal opening rather large, united below, with a thin 

 dark brown line on the outer edges. Color of the mass whitish, slightly tinted with 

 salmon on» the foot, which is long and capable of great extension. 



Remarks. — It inhabits six to twelve inches below the surface of the sand. 



White River, Indiana, D. H. Shaffer. 



Unio tenuissimus, Lea = Sj/mpi/anota tenuissima, Lea. Trans. Amer. Phil. Soc., (2,) vol. iii. pi. 11, 

 fig. 21. Obs. vol. i. p. 67. 



Two only were received, and both males. 



Branchia? large, very thin, rounded below, the inner one slightly the larger, 

 united the whole length of the abdominal sack. Palpi large, suboval, very thin, 

 nearly transverse, united at the upper posterior edges. Mantle very thin, thickened 

 at the margin. Branchial opening large, with small papillae. Anal opening rather 

 small, with very small papilla?. Super-anal opening large, black on the outside 

 edges, united below. Color of the mass whitish. 



White River, Indiana, D. H. Shaffer. 



Unio clavus, Lam. An. sans Vert., vol. vi. p. 74. 



Two males only received. 



Branchial rather large, thin, light liver-brown, rounded below, inner ones the 

 larger, free nearly the whole length of abdominal sack. Mantle rather thick, dirty 

 white, thickened at the margin, which is salmon-colored. Palpi x-ather large, thin, 

 salmon-colored, united one-third down the posterior edges. Branchial opening rather 

 large, with numerous small, light-colored papilla?, the edges being black, with a line 

 of brown inside. Anal opening rather small, with numerous very small, brownish 

 papilla?. Super-anal opening very large, not united below, dark-brown on the edges. 

 Color of the mass salmon, whitish on the abdominal sack, but deep salmon on the 

 foot, adductor muscles and border of the mantle. 



White River, Indiana, D. H. Shaffer. 



Remarks. — The description above was made from a full-grown specimen. The 

 second specimen was an old one, and the color was not deep salmon, but of a dirty 

 white and a light-salmon tint. 



Unio obliqutjs, Lam. (= undalus, Bar.) An. sans Vert., vol. vi. p. 72. 



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



Branchiae large, nearly semicircular, inner ones much the larger, color light liver- 

 brown, free nearly the whole length of the abdominal sack. Palpi rather large, 

 oval, united only at the upper part of the posterior edges. Mantle rather thin, 

 thicker at the margin. Branchial opening large, with numerous small, dark papilla?. 



112 



