8 Trans. Acad. Sci. of St. Louis. 



Unio caliginosus Lea. 



Trans. Am. Philos. Soc, 2d series, Vol. 10, Plate VII, 

 Fig. 21, 1845. 



St. Francis river, Wittsburg ; White river, Carroll 

 county; Ouachita river, Malvern; Saline river, Benton. 

 These localities all furnished numbers of this form and of 

 great perfection. Among the Uniones with which it groups 

 are Unio intercedens Lea, Unio fallax Lea, and Unio subros- 

 trafus Say. The group is widely distributed in the southern 

 States and is characterized by the emargination of the female, 

 on the ventral border. 



Unio capax Green. 



Described by Dr. Green in " Cabinet of Natural His- 

 tory and American Rural Sports," Vol. II, p. 290, Phila., 

 1832. 



Figured as Symphynota globosa Lea, in Trans. Am. 

 Philos. Soc, Vol. V, PI. IV, Fig. 12, 1832. 

 Dr. Green's description has priority by some weeks, though 

 these authors published their diagnoses in the same year. 

 Green's specimens came from the Falls of St. Anthony, and 

 Bayou Teche, La., the localities being widely separated. Dr. 

 Lea's specimens came from the Ohio river, about 150 miles 

 below Louisville. 



The species has occurred in our collections from Arkansas 

 only in the St. Francis river at Wittsburg and is represented 

 by two fine examples. It has the habit of Unio occidens., with 

 which it groups, preferring muddy bottoms and still waters. 

 It is fairly common throughout the Mississippi valley, in the 

 larger streams that flow into the main river. 



A closely related form, from the Altamaha river, Georgia, 

 was described by Dr. Lea under the name of Unio dolabrm- 

 formis^ vide Trans. Am. Philos. Soc, 2d series. Vol. VI, p. 

 103, PI. XXIV, Fig. 113, 1838. It is probably synonymous. 



Unio castaneus Lea. 



Trans. Am. Philos. Soc, Vol. IV, p. 91, PI. XI, Fig. 



21, 1830,. Described from the Alabama river, Alabama. 



Numerous examples of this shell have been taken in the 



